Climatic uncertainty in Himalayan water towers

Abstract

The Himalayan water towers (e.g., Indus, Ganges, and Brahmaputra) play a major role in water resource availability and affect a significant population in the South Asia region. Climatic uncertainty in the region not only hampers progress toward process understanding but also decision making. Observational data sets show uncertainty (standard deviation in mean temperature in data sets) of 0.2 to 0.5°C in winter (January-February-March-April) and the monsoon season (June-July-August-September) air temperature. Observational uncertainty in precipitation in the winter and monsoon seasons ranged between 6 and 17% (with respect to ensemble mean seasonal precipitation) in the Indus, Ganges, and Brahmaputra river basins. The Coordinated Regional Climate Downscaling Experiment (CORDEX) South Asia regional climate models (CORDEX-RCMs) show larger uncertainty (1-3.6°C in temperature and 18-60% in precipitation) than that of the observations. Moreover, RCMs exhibit a large cold bias (6-8°C) and are not able to reproduce the observed warming in the Himalayan water towers. In fact, the CORDEX-RCMs overestimate observed warming by threefold in Ganges and Brahmaputra basins, which raises a question on their reliability on future warming trends in the region. The CORDEX-RCMs overestimate the area that experienced significant warming and fail to reproduce precipitation trends in both magnitude as well as direction. In observational data sets, uncertainty in precipitation and air temperature increases with elevation, which may be associated with sparse observations. However, the CORDEX-RCMs showed larger uncertainty at the lower elevations in both precipitation as well as temperature. The host general circulation models show a better performance in simulating winter climate than the CORDEX-RCMs, which suggest that an improved representation of elevation may not necessarily improve the model's performance. While observations show significant warming in the Indus basin and decline in the monsoon season precipitation in the Ganges basin, reliability of future climate projections and their impacts on water resources in the region will depend on improvements in the models and observations in coming years.

The neglected Indo‐Gangetic Plains low‐level jet and its importance for moisture transport and precipitation during the peak summer monsoon

“…This is further highlighted when simulating the monsoon low over the Ganges basin. Additionally, analysis by Mishra [2015] on various regional climate models agrees with this conclusion. Although the height and geometry of the topography impact the flow over the terrain, we speculate that the production of excessive orographic diabatic heating in CAM is modulated by the adjustments in convective and large-scale parameterizations [O'Brien et al, 2013].…”

“…Res. Lett., 44, 8601-8610, doi:10.1002 orographic precipitation across the HM where model-data disagreement increases toward higher elevation [Mishra, 2015].…”

“…Controversy exists on whether or not the IAM has tipping points [Boos and Storelvmo, 2016;Levermann et al, 2016]. Nevertheless, correctly modeling the IAM in climate models is key to a more reliable future projection [Mishra, 2015] over the region, as well as understanding the IAM spatiotemporal evolution on longer time scales [Molnar et al, 2010]. As a whole, the IAM is a regional expression of a global-scale phenomenon [Trenberth et al, 2000].…”

Future Water Availability from Hindukush-Karakoram-Himalaya upper Indus Basin under Conflicting Climate Change Scenarios

“…It is pertinent to mention here that though CORDEX-SA experiments provide high resolution present and future climate simulations, however, their ability to reproduce the observed hydro-climatology over the steep HKH topography is by hardly any means better than their forcing CMIP5 GCMs, which being consistent to their older versions and downscaled experiments, substantially over-(under-) estimate precipitation (temperatures) and fail to reproduce summer cooling [7,15,16,[82][83][84][85][86][87]. Such cold and wet biases in the CORDEX-SA and their CMIP5 forcing experiments are larger than their projected end of 21st century climatic changes under RCP8.5, indicating huge climatic uncertainty over the UIB [16].…”

Reconciling high-altitude precipitation in the upper Indus basin with glacier mass balances and runoff

“…The quantification of the water balance in space and time is a major challenge due the lack of measurements and the inaccessibility of the terrain. The magnitude and distribution of high-altitude precipitation, which is the driver of the hydrological cycle, is one of its largest unknowns (Hewitt, 2005(Hewitt, , 2007Immerzeel et al, 2013;Mishra, 2015;Ragettli and Pellicciotti, 2012;Winiger et al, 2005). Annual precipitation patterns in the UIB result from the intricate interplay between synoptic scale circulation and valley scale topography-atmosphere interaction resulting in orographic precipitation and funnelling of air movement (Barros et al, 2004;Hewitt, 2013).…”