More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.

http://science.sciencemag.org/content/sci/328/5984/1382.full.pdf

Climate change will affect the Asian water towers.

[1] Using observed data sets mainly for the period 1979–2005, we find that anomalous warming events different from conventional El Nino events occur in the central equatorial Pacific. This unique warming in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. empirical orthogonal function (EOF) analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Nino evolution, the phenomenon is named as El Nino Modoki (pseudo-El Nino) (“Modoki” is a classical Japanese word, which means “a similar but different thing”). The El Nino Modoki involves ocean-atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution, analogous to the Southern Oscillation in the case of El Nino. Hence the total entity is named as El Nino–Southern Oscillation (ENSO) Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season, the impacts over regions such as the Far East including Japan, New Zealand, western coast of United States, etc., are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979–2004 and 1958–1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.

El Niño Modoki and its possible teleconnection

This chapter assesses long-term projections of climate change for the end of the 21st century and beyond, where the forced signal depends on the scenario and is typically larger than the internal variability of the climate system. Changes are expressed with respect to a baseline period of 1986-2005, unless otherwise stated.

Chapter 12 - Long-term climate change: Projections, commitments and irreversibility

Significant climate anomalies persist through the summer (June-August) after El Nino dissipates in spring over the equatorial Pacific. They include the tropical Indian Ocean (TIO) sea surface temperature (SST) warming, increased tropical tropospheric temperature, an anomalous anticyclone over the subtropical northwest Pacific, and increased mei-yu-baiu rainfall over East Asia. The cause of these lingering El Nino effects during summer is investigated using observations and an atmospheric general circulation model (GCM). The results herein indicate that the TIO warming acts like a capacitor anchoring atmospheric anomalies over the Indo-western Pacific Oceans. It causes tropospheric temperature to increase by a moist-adiabatic adjustment in deep convection, emanating a baroclinic Kelvin wave into the Pacific. In the northwest Pacific, this equatorial Kelvin wave induces northeasterly surface wind anomalies, and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone. The GCM results support this Kelvin wave-induced Ekman divergence mechanism. In response to a prescribed SST increase over the TIO, the model simulates the Kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest Pacific. An additional experiment further indicates that the north Indian Ocean warming is most important for the Kelvin wave and northwest Pacific anticyclone, a result corroborated by observations. These results have important implications for the predictability of Indo-western Pacific summer climate: the spatial distribution and magnitude of the TIO warming, rather than simply whether there is an El Nino in the preceding winter, affect summer climate anomalies over the Indo-western Pacific and East Asia.

/pdf/indian-ocean-capacitor-effect-on-indo-western-pacific-6p36vq84fo.pdf

Indian Ocean Capacitor Effect on Indo–Western Pacific Climate during the Summer following El Niño

Surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of El Nino–Southern Oscillation (ENSO) in the tropical Pacific: an eastern-Pacific (EP) type and a central-Pacific (CP) type. An analysis method combining empirical orthogonal function (EOF) analysis and linear regression is used to separate these two types. Correlation and composite analyses based on the principal components of the EOF were performed to examine the structure, evolution, and teleconnection of these two ENSO types. The EP type of ENSO is found to have its SST anomaly center located in the eastern equatorial Pacific attached to the coast of South America. This type of ENSO is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical Indian Ocean. In contrast, the CP type of ENSO has most of its surface wind, SST, and subsurface anomalies confined in the central Pacific and tends to onset, develop, and decay in situ. ...

/pdf/contrasting-eastern-pacific-and-central-pacific-types-of-5eonqt6n8y.pdf

Contrasting Eastern-Pacific and Central-Pacific Types of ENSO

One of the main goals of the ClimaRice II project is to reduce uncertainties in future monsoon projections. The IPRC regional climate model (IPRC_RegCM) has been used to simulate the current and future climates over both Cauvery and Krishna basins. This technical brief summarizes the issues in setting up of a regional climate model such as spin-up time, required climate parameters, selection of model domain and resolution and issues related to lateral boundary conditions. The brief also summarizes the comparison of uncertainties involved in the global climate model and how this will influence the southwest and northeast monsoon seasons over the Indian region. The next brief will investigate the uncertainties in the IPRC_RegCM simulations, particularly over the Cauvery and Krishna basins.

Uncertainties in regional climate change projections: Part I: Choice of global climate models for regional downscaling CLIMARICE II: "Sustaining rice production in a changing climate"


Climate model fidelity in representing ENSO-induced teleconnection is assessed with process-oriented diagnostics that examine a chain of processes, from equatorial Pacific precipitation to the midlatitude circulation pattern over the Pacific–North American regions. Such processes are rarely addressed during model development. Using an upper-tropospheric divergent level, local vorticity gradient of the ambient zonal flow (
) and a restoring force for Rossby waves (
) are estimated, the equivalent barotropic vorticity equation is solved, and an anomalous Rossby wave source (RWS′) quantified. The analysis is applied to AMIP5 and AMIP6 simulations. For a realistic circulation response representation, the hypothesis that models accurately represent the strength and location of RWS′, and spatial variations in 
 is tested. Compared to AMIP5, in AMIP6 there are clear improvements in representing RWS′ and 
. To validate the hypothesis, the analysis identifies two metrics: spatially coherent RWS′ in the subtropical North Pacific, and longitudes of negative 
 over the western-central North Pacific. By projecting these metrics in two and three-dimensional views, improvements or degradations in model versions are apparent. If a model’s fidelity in representing 
 and RWS′ are compromised, then radiated Rossby waves are reflected more equatorward, resulting in zonally elongated circulation anomalies over the central North Pacific. Thus, during climate model development, applying this analysis frequently will keep a regular check on the fidelity of the modeled response to anomalous El Niño convection in conjunction with changing model ambient flow dependencies. This analysis is intended to form a process-oriented diagnostics package, a community contribution to the NOAA Model Diagnostics Task Force.


The seasonal changes in tropical Pacific sea surface temperatures associated with El Niño events can have a significant impact in the atmospheric circulation through the North Pacific and on the annual climate variations over North America. Our skill in predicting these impacts depends critically on the ability of climate models to represent these global-scale connections accurately. We show a number of metrics that describe critical processes along this North Pacific pathway that can be used to examine the progress in climate model skill. In the future, these models could benefit significantly from using these metrics with the end goal of much improved predictions of El Niño–related variability.


H. Annamalai

Papers

Uncertainties in regional climate change projections: Part I: Choice of global climate models for regional downscaling CLIMARICE II: "Sustaining rice production in a changing climate"

ENSO-Induced Teleconnection: Process-Oriented Diagnostics to Assess Rossby Wave Sources and Ambient Flow Properties in Climate Models