Less reliable water availability in the 21st century climate projections

Abstract

The temporal variability of river and soil water affects society at time scales ranging from hourly to decadal. The available water (AW), i.e., precipitation minus evapotranspiration, represents the total water available for runoff, soil water storage change, and ground water recharge. The reliability of AW is defined as the annual range of AW between local wet and dry seasons. A smaller annual range represents greater reliability and a larger range denotes less reliability. Here we assess the reliability of AW in the 21st century climate projections by 20 climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The multimodel consensus suggests less reliable AW in the 21st century than in the 20th century with generally decreasing AW in local dry seasons and increasing AW in local wet seasons. In addition to the canonical perspective from climate models that wet regions will get wetter, this study suggests greater dryness during dry seasons even in regions where the mean climate becomes wetter. Lower emission scenarios show significant advantages in terms of minimizing impacts on AW but do not eliminate these impacts altogether.Summary Modeling of future water availability predicts that wet regions become wetter and dry regions become drier, leading to an increasing likelihood of seasonal droughts and floods in regions where such vulnerability is already high.

A general framework for understanding the response of the water cycle to global warming over land and ocean

“…Recent findings using the CMIP5 archive have been used to argue that the "wet get wetter dry get drier" idea holds for intra-annual (i.e. seasonal) variations in climate model projections out to the year 2100 (Kumar et al, 2014). That study used the same multi-model ensemble mean approach as we have and reported that at a given place, P − E is projected to increase at wet times of the year but is projected to decrease during dry times of the year (Kumar et al, 2014).…”

“…seasonal) differences. One obvious conclusion from the Kumar et al (2014) finding is that one would project the base flow to decrease whilst the high flows should increase. When integrated over the land surface and over a full year, the increases in high flow would have to be larger than the decreases in low flow so that the long-term mean annual runoff could still increase to maintain an overall increase in P − E over land (Table 1).…”

Water availability change in central Belgium for the late 21st century

“…It means the total water available for runoff, soil water storage may change strongly and subsequently ground water recharge (Schuol et al, 2008) may decrease strongly. Kumar et al (2014) also showed a general decrease in available water for dry seasons and increasing available water for wet seasons for Western Europe. The other analysis that was conducted on the net rainfall is obtaining the net rainfall deficit throughout a year (starting at the dry season months) by the end of the century.…”

Terrestrial water flux responses to global warming in tropical rainforest areas

“…Subscripts m and y represent each year and month. This index is similar to the AW index, AW m,y = ( P m,y – ET m,y )/ used by Kumar et al [], but TWFn additionally considers the effects of total runoff. Thus, the TWFn can be regarded as the net water flux (as the fraction of mean precipitation) into the land water storage (i.e., groundwater).…”

“…Increasing temperature and precipitation extremes can substantially alter the terrestrial water cycle, for example, by causing alterations in soil water storage and runoff [ Dirmeyer et al , ; Huang et al , ; Kumar et al , ; Zhang et al , ; Wu et al , ]. The global average dry conditions, and drought areas are likely to enlarge under the global warming [ Dai , ; ; Sheffield et al , ; Cook et al , ; Zhao and Dai , ].…”