Glacial melting in the Tibetan Plateau affects the water resources of millions of people. This study finds that—partly owing to changes in atmospheric circulations and precipitation patterns—the most intensive glacier shrinkage is in the Himalayan region, whereas glacial retreat in the Pamir Plateau region is less apparent.

Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings

Climate strongly influences global wildfire activity, and recent wildfire surges may signal fire weather-induced pyrogeographic shifts. Here we use three daily global climate data sets and three fire danger indices to develop a simple annual metric of fire weather season length, and map spatio-temporal trends from 1979 to 2013. We show that fire weather seasons have lengthened across 29.6 million km2 (25.3%) of the Earth's vegetated surface, resulting in an 18.7% increase in global mean fire weather season length. We also show a doubling (108.1% increase) of global burnable area affected by long fire weather seasons (>1.0 σ above the historical mean) and an increased global frequency of long fire weather seasons across 62.4 million km2 (53.4%) during the second half of the study period. If these fire weather changes are coupled with ignition sources and available fuel, they could markedly impact global ecosystems, societies, economies and climate.

Climate-induced variations in global wildfire danger from 1979-2013

Global warming increases the occurrence probability of hot extremes, and improving the predictability of such events is thus becoming of critical importance. Hot extremes have been shown to be induced by surface moisture deficits in some regions. In this study, we assess whether such a relationship holds at the global scale. We find that wide areas of the world display a strong relationship between the number of hot days in the regions’ hottest month and preceding precipitation deficits. The occurrence probability of an above-average number of hot days is over 70% after precipitation deficits in most parts of South America as well as the Iberian Peninsula and Eastern Australia, and over 60% in most of North America and Eastern Europe, while it is below 30–40% after wet conditions in these regions. Using quantile regression analyses, we show that the impact of precipitation deficits on the number of hot days is asymmetric, i.e. extreme high numbers of hot days are most strongly influenced. This relationship also applies to the 2011 extreme event in Texas. These findings suggest that effects of soil moisture-temperature coupling are geographically more widespread than commonly assumed.

Hot days induced by precipitation deficits at the global scale

The Tibetan Plateau (TP) is undergoing significant warming since the 1950s. During the past two decades, extensive research has been conducted to investigate the climate change on the plateau. This review presents an overview of recent progress on climate change on the TP with the aim of providing a comprehensive understanding of changes in climate variables. Long-term observation data from meteorological stations presented by the published literature were used to show the trends in various climate variables. The TP is overall getting warmer and wetter during the past decades. Temperature is significantly increased, especially since the 1980s. The overall warming rate ranges from 0.16 to 0.67°C decade−1 since the 1950s during different periods. The TP shows a uniform warming trend with the most significant warming in the northern part. Precipitation is slightly increased, and the spatial pattern of changes in precipitation is variable. The annual precipitation is increasing in most areas of the TP. Some subregions are becoming wetter, while some subregions are becoming drier. Pan evaporation, reference evapotranspiration, and potential evapotranspiration have been found to decrease since the 1960s. Actual evapotranspiration is significantly increased since the 1960s. Wind speed and sunshine duration increased up to the 1970s and then decreased significantly afterwards. Relative humidity fluctuated up and down to the end of the 1990s and appeared to decrease afterwards. Vapor pressure deficit shows an overall increasing trend since the 1970s. Causes of changes in the climate variables are presented, and future research directions are recommended.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2015JD024728

Review on climate change on the Tibetan Plateau during the last half century

Trees are the living foundations on which most terrestrial biodiversity is built. Central to the success of trees are their woody bodies, which connect their elevated photosynthetic canopies with the essential belowground activities of water and nutrient acquisition. The slow construction of these carbon-dense, woody skeletons leads to a slow generation time, leaving trees and forests highly susceptible to rapid changes in climate. Other long-lived, sessile organisms such as corals appear to be poorly equipped to survive rapid changes, which raises questions about the vulnerability of contemporary forests to future climate change. The emerging view that, similar to corals, tree species have rather inflexible damage thresholds, particularly in terms of water stress, is especially concerning. This Review examines recent progress in our understanding of how the future looks for forests growing in a hotter and drier atmosphere.

Hanging by a thread? Forests and drought

Estimating long-term trends and short-term amplitudes requires reliable temperature (Temp) observations in the pre-industrial period when few in situ observations existed in the Arctic. Tree-ring materials are most available and used to reconstruct past Arctic Temp variations. However, most previous studies incorporated materials that are insensitive to local Temp variabilities. The derived reconstruction qualities are low (indicated by low calibration R2), and the uncertainties inherent in the various detrending methodologies are unknown. To reconstruct Arctic (N60°–N90°) summer (June–August) Temp in 1850–1900 and variations over the past centuries, we screened 1116 tree-ring width and tree-ring density records and applied four detrending functions (sf-RCS, RCS, MOD, and spline). In total, 338–396 records show significant correlations (p < 0.05) with the Climate Research Unit (CRU) Temp of the corresponding grid point. These records were selected and combined into a proxy record. The achieved Arctic summer Temp reconstruction explained 45–57% of the instrumental summer Temp variance since 1950. The 2012–2021 summer Arctic warming amplitudes (1.42–1.74 °C) estimated by Temp anomaly datasets extending back to 1850 are within the range derived from our reconstructions, despite using various detrending methods. These findings could suggest the Berkeley and HadCRU5 datasets interpolating Temp from a few (6–73) meteorological stations could still represent the mean Arctic Temp variation in 1850–1900, and the updated reconstruction can be used as a reliable reference for 1550–2007 Arctic summer Temp history.

/pdf/estimating-summer-arctic-warming-amplitude-relative-to-pre-1fp6cd2a.pdf

Estimating Summer Arctic Warming Amplitude Relative to Pre-Industrial Levels Using Tree Rings


Precipitation events should be characterized using data with high temporal resolution, such as hourly precipitation. Event-based evaluation can provide more information than the traditional equal-time-interval method by considering precipitation intermittency. This study focuses on the performance of hourly gauge observations and ERA5 products based on precipitation events in eastern China during 1979–2015. The annual frequency, duration, amount, and intensity of precipitation events are compared, and the statistics of precipitation events with different durations are also evaluated. Results show that ERA5 estimated more annual precipitation events and longer duration compared to the gauge observations, with relative deviation values of 48.75% and 49.22% at the national scale. Precipitation intensity and amount estimated by ERA5 based on precipitation events were less than those obtained from gauge observations, and the discrepancies in low-latitude regions were greater than those in high-latitude areas. The frequency of precipitation events decreased exponentially with duration for both ERA5 and gauge observations, but generally the value for the former was larger than for the latter. The statistics related to precipitation events showed smaller trends for ERA5 than for gauge observations, i.e., −0.13 h decade−1 and −0.17 mm decade−1 for the trends of duration and amount in ERA5, which contrasts with 0.03 h decade−1 and 0.14 mm decade−1 for gauge observations, respectively. These results can provide a reference for improving the parameterization scheme of the precipitation triggering mechanism in the process of model simulation.

Chunming Shi

Papers

Estimating Summer Arctic Warming Amplitude Relative to Pre-Industrial Levels Using Tree Rings

Validation of Precipitation Events in ERA5 to Gauge Observations during Warm Seasons over Eastern China