Showing papers on "Precipitation published in 2017"

Climatologies at high resolution for the earth’s land surface areas

Abstract: High-resolution information on climatic conditions is essential to many applications in environmental and ecological sciences. Here we present the CHELSA (Climatologies at high resolution for the earth’s land surface areas) data of downscaled model output temperature and precipitation estimates of the ERA-Interim climatic reanalysis to a high resolution of 30 arc sec. The temperature algorithm is based on statistical downscaling of atmospheric temperatures. The precipitation algorithm incorporates orographic predictors including wind fields, valley exposition, and boundary layer height, with a subsequent bias correction. The resulting data consist of a monthly temperature and precipitation climatology for the years 1979–2013. We compare the data derived from the CHELSA algorithm with other standard gridded products and station data from the Global Historical Climate Network. We compare the performance of the new climatologies in species distribution modelling and show that we can increase the accuracy of species range predictions. We further show that CHELSA climatological data has a similar accuracy as other products for temperature, but that its predictions of precipitation patterns are better. Machine-accessible metadata file describing the reported data (ISA-Tab format)

The future intensification of hourly precipitation extremes

Abstract: Climate change is causing increases in extreme rainfall across the United States. This study uses observations and high-resolution modelling to show that rainfall changes related to rising temperatures depend on the available atmospheric moisture. Extreme precipitation intensities have increased in all regions of the Contiguous United States (CONUS)1 and are expected to further increase with warming at scaling rates of about 7% per degree Celsius (ref. 2), suggesting a significant increase of flash flood hazards due to climate change. However, the scaling rates between extreme precipitation and temperature are strongly dependent on the region, temperature3, and moisture availability4, which inhibits simple extrapolation of the scaling rate from past climate data into the future5. Here we study observed and simulated changes in local precipitation extremes over the CONUS by analysing a very high resolution (4 km horizontal grid spacing) current and high-end climate scenario that realistically simulates hourly precipitation extremes. We show that extreme precipitation is increasing with temperature in moist, energy-limited, environments and decreases abruptly in dry, moisture-limited, environments. This novel framework explains the large variability in the observed and modelled scaling rates and helps with understanding the significant frequency and intensity increases in future hourly extreme precipitation events and their interaction with larger scales.

Understanding the regional pattern of projected future changes in extreme precipitation

Abstract: Regional projections of daily extreme precipitation are uncertain, but can be decomposed into thermodynamic and dynamic contributions to improve understanding While thermodynamics alone uniformly increase extreme precipitation, dynamical processes introduce regional variations

Precipitation variability increases in a warmer climate

Abstract: Understanding changes in precipitation variability is essential for a complete explanation of the hydrologic cycle’s response to warming and its impacts. While changes in mean and extreme precipitation have been studied intensively, precipitation variability has received less attention, despite its theoretical and practical importance. Here, we show that precipitation variability in most climate models increases over a majority of global land area in response to warming (66% of land has a robust increase in variability of seasonal-mean precipitation). Comparing recent decades to RCP8.5 projections for the end of the 21st century, we find that in the global, multi-model mean, precipitation variability increases 3–4% K−1 globally, 4–5% K−1 over land and 2–4% K−1 over ocean, and is remarkably robust on a range of timescales from daily to decadal. Precipitation variability increases by at least as much as mean precipitation and less than moisture and extreme precipitation for most models, regions, and timescales. We interpret this as being related to an increase in moisture which is partially mitigated by weakening circulation. We show that changes in observed daily variability in station data are consistent with increased variability.

Continental-scale convection-permitting modeling of the current and future climate of North America

Abstract: Orographic precipitation and snowpack provide a vital water resource for the western U.S., while convective precipitation accounts for a significant part of annual precipitation in the eastern U.S. As a result, water managers are keenly interested in their fate under climate change. However, previous studies of water cycle changes in the U.S. have been conducted with climate models of relatively coarse resolution, leading to potential misrepresentation of key physical processes. This paper presents results from a high-resolution climate change simulation that permits convection and resolves mesoscale orography at 4-km grid spacing over much of North America using the Weather Research and Forecasting (WRF) model. Two 13-year simulations were performed, consisting of a retrospective simulation (October 2000–September 2013) with initial and boundary conditions from ERA-interim and a future climate sensitivity simulation with modified reanalysis-derived initial and boundary conditions through adding the CMIP5 ensemble-mean high-end emission scenario climate change. The retrospective simulation is evaluated by validating against Snowpack Telemetry (SNOTEL) and an ensemble of gridded observational datasets. It shows overall good performance capturing the annual/seasonal/sub-seasonal precipitation and surface temperature climatology except for a summer dry and warm bias in the central U.S. In particular, the WRF seasonal precipitation agrees with SNOTEL observations within a few percent over the mountain ranges, providing confidence in the model’s estimation of western U.S. seasonal snowfall and snowpack. The future climate simulation forced with warmer and moister perturbed boundary conditions enhances annual and winter-spring-fall seasonal precipitation over most of the contiguous United States (CONUS), but suppresses summertime precipitation in the central U.S. The WRF-downscaled climate change simulations provide a high-resolution dataset (i.e., High-Resolution CONUS downscaling, HRCONUS) to the community for studying one possible scenario of regional climate changes and impacts.

Towards a rain-dominated Arctic

Abstract: Arctic precipitation is projected to increase and this study shows that rainfall will become the dominant phase of precipitation, with a decrease in snowfall across all seasons. Climate models project a strong increase in Arctic precipitation over the coming century1, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat2. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow3. However, little is known about future changes in the distributions of rainfall and snowfall in the Arctic. Here we use 37 state-of-the-art climate models in standardized twenty-first-century (2006–2100) simulations4 to show a decrease in average annual Arctic snowfall (70°–90° N), despite the strong precipitation increase. Rain is projected to become the dominant form of precipitation in the Arctic region (2091–2100), as atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rainfall and snowfall will heavily impact Arctic hydrology (for example, river discharge, permafrost melt)5,6,7, climatology (for example, snow, sea-ice albedo and melt)8,9 and ecology (for example, water and food availability)5,10.

Relative contribution of monsoon precipitation and pumping to changes in groundwater storage in India

Abstract: The depletion of groundwater resources threatens food and water security in India. However, the relative influence of groundwater pumping and climate variability on groundwater availability and storage remains unclear. Here we show from analyses of satellite and local well data spanning the past decade that long-term changes in monsoon precipitation are driving groundwater storage variability in most parts of India either directly by changing recharge or indirectly by changing abstraction. We find that groundwater storage has declined in northern India at the rate of 2 cm yr−1 and increased by 1 to 2 cm yr−1 in southern India between 2002 and 2013. We find that a large fraction of the total variability in groundwater storage in north-central and southern India can be explained by changes in precipitation. Groundwater storage variability in northwestern India can be explained predominantly by variability in abstraction for irrigation, which is in turn influenced by changes in precipitation. Declining precipitation in northern India is linked to Indian Ocean warming, suggesting a previously unrecognized teleconnection between ocean temperatures and groundwater storage. Groundwater storage has declined in northern India and increased in southern India over the past decade. Trend analysis shows that much of this variability can be explained by changes in irrigation in response to monsoon precipitation.

The global distribution and dynamics of surface soil moisture

Abstract: Surface soil moisture has a direct impact on food security, human health and ecosystem function. It also plays a key role in the climate system, and the development and persistence of extreme weather events such as droughts, floods and heatwaves. However, sparse and uneven observations have made it difficult to quantify the global distribution and dynamics of surface soil moisture. Here we introduce a metric of soil moisture memory and use a full year of global observations from NASA’s Soil Moisture Active Passive mission to show that surface soil moisture—a storage believed to make up less than 0.001% of the global freshwater budget by volume, and equivalent to an, on average, 8-mm thin layer of water covering all land surfaces—plays a significant role in the water cycle. Specifically, we find that surface soil moisture retains a median 14% of precipitation falling on land after three days. Furthermore, the retained fraction of the surface soil moisture storage after three days is highest over arid regions, and in regions where drainage to groundwater storage is lowest. We conclude that lower groundwater storage in these regions is due not only to lower precipitation, but also to the complex partitioning of the water cycle by the surface soil moisture storage layer at the land surface. Soils have the capacity to store water at the land–atmosphere interface. Analysis of global satellite data suggests that significant precipitation can be retained by soils, leading to even less groundwater storage in water-starved regions.

Land Surface Precipitation in MERRA-2

Abstract: The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), features several major advances from the original MERRA reanalysis, including the use, outside of high latitudes, of observations-based precipitation data products to correct the precipitation falling on the land surface in the MERRA-2 system. The method for merging the observed precipitation into MERRA-2 has been refined from that of the (land-only) MERRA-Land reanalysis. This paper describes the method and evaluates the MERRA-2 land surface precipitation. Compared to monthly GPCPv2.2 observations, the corrected MERRA-2 precipitation (M2CORR) is better than the precipitation generated by the atmospheric models within the cycling MERRA-2 and MERRA systems. M2CORR is also better than MERRA-Land precipitation over Africa because in MERRA-2 a merged satellite–gauge precipitation product is used instead of the gauge-only data used for MERRA-Land. Compared to 3-hourly TRMM observations, the M2CORR diurnal cycle ha...

Precipitation in a warming world: Assessing projected hydro-climate changes in California and other Mediterranean climate regions

Abstract: In most Mediterranean climate (MedClim) regions around the world, global climate models (GCMs) consistently project drier futures. In California, however, projections of changes in annual precipitation are inconsistent. Analysis of daily precipitation in 30 GCMs reveals patterns in projected hydrometeorology over each of the five MedClm regions globally and helps disentangle their causes. MedClim regions, except California, are expected to dry via decreased frequency of winter precipitation. Frequencies of extreme precipitation, however, are projected to increase over the two MedClim regions of the Northern Hemisphere where projected warming is strongest. The increase in heavy and extreme precipitation is particularly robust over California, where it is only partially offset by projected decreases in low-medium intensity precipitation. Over the Mediterranean Basin, however, losses from decreasing frequency of low-medium-intensity precipitation are projected to dominate gains from intensifying projected extreme precipitation. MedClim regions are projected to become more sub-tropical, i.e. made dryer via pole-ward expanding subtropical subsidence. California's more nuanced hydrological future reflects a precarious balance between the expanding subtropical high from the south and the south-eastward extending Aleutian low from the north-west. These dynamical mechanisms and thermodynamic moistening of the warming atmosphere result in increased horizontal water vapor transport, bolstering extreme precipitation events.

How much runoff originates as snow in the western United States, and how will that change in the future?

Abstract: In the western United States, the seasonal phase of snow storage bridges between winter-dominant precipitation and summer-dominant water demand. The critical role of snow in water supply has been frequently quantified using the ratio of snowmelt-derived runoff to total runoff. However, current estimates of the fraction of annual runoff generated by snowmelt are not based on systematic analyses. Here based on hydrological model simulations and a new snowmelt tracking algorithm, we show that 53% of the total runoff in the western United States originates as snowmelt, despite only 37% of the precipitation falling as snow. In mountainous areas, snowmelt is responsible for 70% of the total runoff. By 2100, the contribution of snowmelt to runoff will decrease by one third for the western U.S. in the Intergovernmental Panel on Climate Change Representative Concentration Pathway 8.5 scenario. Snowmelt-derived runoff currently makes up two thirds of the inflow to the region's major reservoirs. We argue that substantial impacts on water supply are likely in a warmer climate.

Increased rainfall volume from future convective storms in the US

Abstract: Mesoscale convective system (MCS)-organized convective storms with a size of ~100 km have increased in frequency and intensity in the USA over the past 35 years 1 , causing fatalities and economic losses 2 . However, their poor representation in traditional climate models hampers the understanding of their change in the future 3 . Here, a North American-scale convection-permitting model which is able to realistically simulate MSCs 4 is used to investigate their change by the end-of-century under RCP8.5 (ref. 5 ). A storm-tracking algorithm 6 indicates that intense summertime MCS frequency will more than triple in North America. Furthermore, the combined effect of a 15–40% increase in maximum precipitation rates and a significant spreading of regions impacted by heavy precipitation results in up to 80% increases in the total MCS precipitation volume, focussed in a 40 km radius around the storm centre. These typically neglected increases substantially raise future flood risk. Current investments in long-lived infrastructures, such as flood protection and water management systems, need to take these changes into account to improve climate-adaptation practices. Limitations with climate models have previously prevented accurate diagnosis of future changes in mesoscale convective systems (MCSs). A convection-permitting model now indicates that summer MCSs will triple by 2100 in the United States, with a corresponding increase in rainfall rates and areal extent.

Precipitation change in the United States

Abstract: Climate Science Special Report U.S. Global Change Research Program Recommended Citation for Chapter Easterling, D.R., K.E. Kunkel, J.R. Arnold, T. Knutson, A.N. LeGrande, L.R. Leung, R.S. Vose, D.E. Waliser, and M.F. Wehner, 2017: Precipitation change in the United States. In: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 207-230, doi: 10.7930/J0H993CC. KEY FINDINGS

The peak structure and future changes of the relationships between extreme precipitation and temperature

Abstract: Theoretical models predict that, in the absence of moisture limitation, extreme precipitation intensity could exponentially increase with temperatures at a rate determined by the Clausius-Clapeyron (C-C) relationship. Climate models project a continuous increase of precipitation extremes for the twenty-first century over most of the globe. However, some station observations suggest a negative scaling of extreme precipitation with very high temperatures, raising doubts about future increase of precipitation extremes. Here we show for the present-day climate over most of the globe,the curve relating daily precipitation extremes with local temperatures has a peak structure, increasing as expected at the low medium range of temperature variations but decreasing at high temperatures. However, this peak-shaped relationship does not imply a potential upper limit for future precipitation extremes. Climate models project both the peak of extreme precipitation and the temperature at which it peaks (T(sub peak)) will increase with warming; the two increases generally conform to the C-C scaling rate in mid- and high-latitudes,and to a super C-C scaling in most of the tropics. Because projected increases of local mean temperature (T(sub mean)) far exceed projected increases of T(sub peak) over land, the conventional approach of relating extreme precipitation to T(sub mean) produces a misleading sub-C-C scaling rate.

Extreme winds and precipitation during landfall of atmospheric rivers

Abstract: Atmospheric rivers—long, narrow filaments of large integrated water vapour transport—are associated with weather and water extremes, such as precipitation extremes and flooding in western North America and northern Europe. Here we apply a global detection algorithm for atmospheric rivers to reanalysis data during 1997–2014 to investigate the impact of atmospheric rivers on wind extremes as well as precipitation extremes. We find that atmospheric rivers are associated with up to half of the extreme events in the top 2% of the precipitation and wind distribution, across most mid-latitude regions globally. Landfalling atmospheric rivers are associated with about 40–75% of extreme wind and precipitation events over 40% of the world’s coastlines. Atmospheric rivers are associated with a doubling or more of the typical wind speed compared to all storm conditions, and a 50–100% increase in the wind and precipitation values for extreme events. We also find that the majority of extreme wind events catalogued between 1997 and 2013 over Europe with billion US dollar losses were associated with atmospheric rivers. We conclude that landfalling atmospheric rivers can represent a significant hazard around the globe, because of their association with not only extreme precipitation, but also extreme winds. Atmospheric rivers have been associated with extreme rainfall events. A global detection algorithm, applied to reanalysis data, suggests that they contribute substantially to extremes in wind as well as precipitation along coasts globally.

Over 5,000 years of ensemble future climate simulations by 60-km global and 20-km regional atmospheric models

Abstract: An unprecedentedly large ensemble of climate simulations with a 60-km atmospheric general circulation model and dynamical downscaling with a 20-km regional climate model has been performed to obtain probabilistic future projections of low-frequency local-scale events. The climate of the latter half of the twentieth century, the climate 4 K warmer than the preindustrial climate, and the climate of the latter half of the twentieth century without historical trends associated with the anthropogenic effect are each simulated for more than 5,000 years. From large ensemble simulations, probabilistic future changes in extreme events are available directly without using any statistical models. The atmospheric models are highly skillful in representing localized extreme events, such as heavy precipitation and tropical cyclones. Moreover, mean climate changes in the models are consistent with those in phase 5 of the Coupled Model Intercomparison Project (CMIP5) ensembles. Therefore, the results enable the a...

Evaluating the Hydrological Cycle over Land Using the Newly-Corrected Precipitation Climatology from the Global Precipitation Climatology Centre (GPCC)

Abstract: The 2015 release of the precipitation climatology from the Global Precipitation Climatology Centre (GPCC) for 1951–2000, based on climatological normals of about 75,100 rain gauges, allows for quantification of mean land surface precipitation as part of the global water cycle. In GPCC’s 2011-release, a bulk climatological correction was applied to compensate for gauge undercatch. In this paper we derive an improved correction approach based on the synoptic weather reports for the period 1982–2015. The compared results show that the climatological approach tends to overestimate the correction for Central and Eastern Europe, especially in the northern winter, and in other regions throughout the year. Applying the mean weather-dependent correction to the GPCC’s uncorrected precipitation climatology for 1951–2000 gives a value of 854.7 mm of precipitation per year (excluding Antarctica) or 790 mm for the global land surface. The warming of nearly 1 K relative to pre-industrial temperatures is expected to be accompanied by a 2%–3% increase in global (land and ocean) precipitation. However, a comparison of climatology for 30-year reference periods from 1931–1960 up to 1981–2010 reveals no significant trend for land surface precipitation. This may be caused by the large variability of precipitation, the varying data coverage over time and other issues related to the sampling of rain-gauge networks. The GPCC continues to enlarge and further improve the quality of its database, and will generate precipitation analyses with homogeneous data coverage over time. Another way to reduce the sampling issues is the combination of rain gauge-based analyses with remote sensing (i.e., satellite or radar) datasets.

Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments

Abstract: Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta-analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.

Regionally strong feedbacks between the atmosphere and terrestrial biosphere

Abstract: The terrestrial biosphere and atmosphere interact through a series of feedback loops. Variability in terrestrial vegetation growth and phenology can modulate fluxes of water and energy to the atmosphere, and thus affect the climatic conditions that in turn regulate vegetation dynamics. Here we analyze satellite observations of solar-induced fluorescence, precipitation, and radiation using a multivariate statistical technique. We find that biosphere-atmosphere feedbacks are globally widespread and regionally strong: they explain up to 30% of precipitation and surface radiation variance. Substantial biosphere-precipitation feedbacks are often found in regions that are transitional between energy and water limitation, such as semi-arid or monsoonal regions. Substantial biosphere-radiation feedbacks are often present in several moderately wet regions and in the Mediterranean, where precipitation and radiation increase vegetation growth. Enhancement of latent and sensible heat transfer from vegetation accompanies this growth, which increases boundary layer height and convection, affecting cloudiness, and consequently incident surface radiation. Enhanced evapotranspiration can increase moist convection, leading to increased precipitation. Earth system models underestimate these precipitation and radiation feedbacks mainly because they underestimate the biosphere response to radiation and water availability. We conclude that biosphere-atmosphere feedbacks cluster in specific climatic regions that help determine the net CO2 balance of the biosphere.

Rising Precipitation Extremes across Nepal

Abstract: As a mountainous country, Nepal is most susceptible to precipitation extremes and related hazards, including severe floods, landslides and droughts that cause huge losses of life and property, impact the Himalayan environment, and hinder the socioeconomic development of the country. Given that the countrywide assessment of such extremes is still lacking, we present a comprehensive picture of prevailing precipitation extremes observed across Nepal. First, we present the spatial distribution of daily extreme precipitation indices as defined by the Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI) from 210 stations over the period of 1981–2010. Then, we analyze the temporal changes in the computed extremes from 76 stations, featuring long-term continuous records for the period of 1970–2012, by applying a non-parametric Mann−Kendall test to identify the existence of a trend and Sen’s slope method to calculate the true magnitude of this trend. Further, the local trends in precipitation extremes have been tested for their field significance over the distinct physio-geographical regions of Nepal, such as the lowlands, middle mountains and hills and high mountains in the west (WL, WM and WH, respectively), and likewise, in central (CL, CM and CH) and eastern (EL, EM and EH) Nepal. Our results suggest that the spatial patterns of high-intensity precipitation extremes are quite different to that of annual or monsoonal precipitation. Lowlands (Terai and Siwaliks) that feature relatively low precipitation and less wet days (rainy days) are exposed to high-intensity precipitation extremes. Our trend analysis suggests that the pre-monsoonal precipitation is significantly increasing over the lowlands and CH, while monsoonal precipitation is increasing in WM and CH and decreasing in CM, CL and EL. On the other hand, post-monsoonal precipitation is significantly decreasing across all of Nepal while winter precipitation is decreasing only over the WM region. Both high-intensity precipitation extremes and annual precipitation trends feature east−west contrast, suggesting significant increase over the WM and CH region but decrease over the EM and CM regions. Further, a significant positive trend in the number of consecutive dry days but significant negative trend in the number of wet (rainy) days are observed over the whole of Nepal, implying the prolongation of the dry spell across the country. Overall, the intensification of different precipitation indices over distinct parts of the country indicates region-specific risks of floods, landslides and droughts. The presented findings, in combination with population and environmental pressures, can support in devising the adequate region-specific adaptation strategies for different sectors and in improving the livelihood of the rural communities in Nepal.

Uncertainties in historical changes and future projections of drought. Part I: estimates of historical drought changes

Abstract: How drought may change in the future are of great concern as global warming continues. In Part I of this study, we examine the uncertainties in estimating recent drought changes. Substantial uncertainties arise in the calculated Palmer Drought Severity Index (PDSI) with Penman-Monteith potential evapotranspiraiton (PDSI_pm) due to different choices of forcing data (especially for precipitation, solar radiation and wind speed) and the calibration period. After detailed analyses, we recommend using the Global Precipitation Climatology Centre (GPCC) or the Global Precipitation Climatology (GPCP) datasets over other existing land precipitation products due to poor data coverage in the other datasets since the 1990s. We also recommend not to include the years after 1980 in the PDSI calibration period to avoid including the anthropogenic climate change as part of the natural variability used for calibration. Consistent with reported declines in pan evaporation, our calculated potential evapotranspiration (PET) shows negative or small trends since 1950 over the United States, China, and other regions, and no global PET trends from 1950 to 1990. Updated precipitation and streamflow data and the self-calibrated PDSI_pm all show consistent drying during 1950–2012 over most Africa, East and South Asia, southern Europe, eastern Australia, and many parts of the Americas. While these regional drying trends resulted primarily from precipitation changes related to multi-decadal oscillations in Pacific sea surface temperatures, rapid surface warming and associated increases in surface vapor pressure deficit since the 1980s have become an increasingly important cause of widespread drying over land.

Pan-European Seasonal Trends and recent changes of drought frequency and severity

Abstract: In the last decades drought has become one of the natural disasters with most relevant impacts in Europe and this not only in water scarce areas such as the Mediterranean that are inclined to such events. As a complex natural phenomenon, drought is characterized by many hydro-meteorological aspects, a large variety of possible impacts and definitions. This study focuses on meteorological drought, investigated by using indicators that include precipitation and potential evapotranspiration (PET), i.e. the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI). These indicators account for the lack of precipitation and the drying effects of hot temperatures and in this study have been computed for short-accumulation periods (3-month) to capture the seasonality of droughts. The input variables, monthly precipitation and temperature for 1950–2015, stem from daily gridded E-OBS data and indicators were computed on regular grids spanning over the whole of Europe. PET was calculated from minimum and maximum temperatures using the Hargreaves-Samani formulation. Monthly precipitation and PET have then been used to compute the SPI-3 and the SPEI-3 time series. From these series drought events were defined at seasonal scale and trends of frequency and severity of droughts and extreme droughts were analyzed for the periods 1950–2015 and 1981–2015. According to the SPI (driven by precipitation), results show a statistically significant tendency towards less frequent and severe drought events over North-Eastern Europe, especially in winter and spring, and a moderate opposite tendency over Southern Europe, especially in spring and summer. According to the SPEI (driven by precipitation and temperature), Northern Europe shows similar wetting patterns, while Southern and Eastern Europe show a more remarkable drying tendency, especially in summer and autumn. Both for frequency and severity, the evolution towards drier conditions is more relevant in the last three decades over Central Europe in spring, the Mediterranean area in summer, and Eastern Europe in autumn.

Recent Changes in the Moisture Source of Precipitation over the Tibetan Plateau

Abstract: Evidence has suggested a wetting trend over part of the Tibetan Plateau (TP) in recent decades, although there are large uncertainties in this trend due to sparse observations. Examining the change in the moisture source for precipitation over a region in the TP with the most obvious increasing precipitation trend may help understand the precipitation change. This study applied the modified Water Accounting Model with two atmospheric reanalyses, ground-observed precipitation, and evaporation from a land surface model to investigate the change in moisture source of the precipitation over the targeted region. The study estimated that on average more than 69% and more than 21% of the moisture supply to precipitation over the targeted region came from land and ocean, respectively. The moisture transports from the west of the TP by the westerlies and from the southwest by the Indian summer monsoon likely contributed the most to precipitation over the targeted region. The moisture from inside the region...

Improved modeling of snow and glacier melting by a progressive two‐stage calibration strategy with GRACE and multisource data: How snow and glacier meltwater contributes to the runoff of the Upper Brahmaputra River basin?

Abstract: Snow and glacier melting and accumulation are important processes of the hydrological cycle in the cryosphere, e.g., high-mountain areas. Glaciers and snow cover respond to climate change notably over the Tibetan Plateau (TP) as the Earth's Third Pole where complex topography and lack of ground-based observations result in knowledge gaps in hydrological processes and large uncertainties in model output. This study develops a snow and glacier melt model for a distributed hydrological model (Coupled Routing and Excess Storage model, CREST) using the Upper Brahmaputra River (UBR) basin in the TP as a case study. Satellite and ground-based precipitation and land surface temperature are jointly used as model forcing. A progressive two-stage calibration strategy is developed to derive model parameters, i.e., (1) snow melting processes (stage I) and (2) glacier melting and runoff generation and routing using multisource data (stage II). Stage-I calibration is performed using the MODIS snow cover area (SCA) product and a blending snow water equivalent (SWE) product combined with partial in situ measurements. Stage-II calibration is based on Gravity Recovery and Climate Experiment (GRACE) satellite-derived total water storage (TWS) changes and streamflow observed at a gauging station of the lower reach of the UBR. Results indicate that the developed two-stage calibration method provides more reliable streamflow, snow (both SCA and SWE), and TWS change simulations against corresponding observations than commonly used methods based on streamflow and/or SCA performance. The simulated TWS time series shows high consistency with GRACE counterparts for the study period 2003–2014, and overestimated melting rates and contributions of glacier meltwater to runoff in previous studies are improved to some degree by the developed model and calibration strategy. Snow and glacier runoff contributed 10.6% and 9.9% to the total runoff, and the depletion rate of glacier mass was ∼ −10 mm/a (∼ −2.4 Gt/a, Gt/a is gigaton (km3 of water) per year) over the UBR basin during the study period. This study is valuable in examining the impacts of climate change on hydrological processes of cryospheric regions and providing an improved approach for simulating more reliable hydrological variables over the UBR basin and potentially similar regions globally.

Evaluation of current and projected Antarctic precipitation in CMIP5 models

Abstract: On average, the models in the Fifth Climate Model Intercomparison Project archive predict an increase in Antarctic precipitation from 5.5 to 24.5 % between 1986–2005 and 2080–2099, depending on greenhouse gas emissions scenarios. This translates into a moderation of future sea level rise ranging from −19 to −71 mm between 2006 and 2099. However, comparison with CloudSat and ERA-Interim data show that almost all the models overestimate current Antarctic precipitation, some by more than 100 %. If only the models that agree with CloudSat data within 20 % of error are considered, larger precipitation changes (from 7.4 to 29.3 %) and impact on sea level (from −25 to −85 mm) are predicted. A common practice of averaging all models to evaluate climate projections thus leads to a significant underestimation of the contribution of Antarctic precipitation to future sea level. Models simulate, on average, a 7.4 %/°C precipitation change with surface temperature warming. The models in better agreement with CloudSat observations for Antarctic snowfall predict, on average, larger temperature and Antarctic sea ice cover changes, which could explain the larger changes in Antarctic precipitation simulated by these models. The agreement between the models, CloudSat data and ERA-Interim is generally less in the interior of Antarctica than at the peripheries, but the interior is also where climate change will induce the smallest absolute change in precipitation. About three-quarters of the impact on sea level will result from precipitation change over the half most peripheral and lowest elevation part of the surface of Antarctica.

Warming combined with more extreme precipitation regimes modifies the water sources used by trees.

Abstract: Summary The persistence of vegetation under climate change will depend on a plant's capacity to exploit water resources. We analyzed water source dynamics in pinon pine and juniper trees subjected to precipitation reduction, atmospheric warming, and to both simultaneously. Pinon and juniper exhibited different and opposite shifts in water uptake depth in response to experimental stress and background climate over 3 yr. During a dry summer, juniper responded to warming with a shift to shallow water sources, whereas pinon pine responded to precipitation reduction with a shift to deeper sources in autumn. In normal and wet summers, both species responded to precipitation reduction, but juniper increased deep water uptake and pinon increased shallow water uptake. Shifts in the utilization of water sources were associated with reduced stomatal conductance and photosynthesis, suggesting that belowground compensation in response to warming and water reduction did not alleviate stress impacts for gas exchange. We have demonstrated that predicted climate change could modify water sources of trees. Warming impairs juniper uptake of deep sources during extended dry periods. Precipitation reduction alters the uptake of shallow sources following extended droughts for pinon. Shifts in water sources may not compensate for climate change impacts on tree physiology.

A revival of Indian summer monsoon rainfall since 2002

Abstract: A significant reduction in summer monsoon rainfall has been observed in northern central India during the second half of the twentieth century, threatening water security and causing widespread socio-economic impacts. Here, using various observational data sets, we show that monsoon rainfall has increased in India at 1.34 mm d−1 decade−1 since 2002. This apparent revival of summer monsoon precipitation is closely associated with a favourable land–ocean temperature gradient, driven by a strong warming signature over the Indian subcontinent and slower rates of warming over the Indian Ocean. The continental Indian warming is attributed to a reduction of low cloud due to decreased ocean evaporation in the Arabian Sea, and thus decreased moisture transport to India. Global climate models fail to capture the observed rainfall revival and corresponding trends of the land–ocean temperature gradient, with implications for future projections of the Indian monsoon. Since ∼1950, a significant reduction in Indian monsoon rainfall has been observed. Here, it is shown that land–ocean temperature contrasts have produced more favourable monsoon conditions since 2002, reviving summer monsoon rainfall over India.