THE PROJECTED HYDROLOGIC CYCLE UNDER THE SCENARIO OF 936 PPM CO2 IN 2100: A SYNTHESIS

A host of environmental consequences will result from global warming, but arguably the effect on water resources is one of the most consequential. We synthesized results of published modelling studies that examined the groundwater system and hydrologic cycle under the Representative Concentration Pathway (RCP) 8.5 scenario (CO₂ at 936-ppm level at year 2100). Natural replenishment of groundwater occurs predominantly from infiltration of precipitation and surface impoundments. Therefore, we reviewed a changed hydrologic cycle under RCP 8.5 in terms of influence from (1) precipitation, evapotranspiration, and soil moisture; (2) surface water and its interaction with groundwater; (3) extreme hydrologic events, and (4) teleconnection patterns. The general pattern of climate impact on groundwater resources follows the precipitation pattern with depletion in tropical and/or subtropical regions and with increase in the high-latitude regions of the Northern and Southern Hemispheres. However, regional variability also corresponds to the heterogenous impact of climate changes on regional distribution of precipitation and evapotranspiration, localized interaction between surface water and groundwater, and distances from the oceans with rising sea level. The decline of the water table in many areas may seriously reduce irrigated crop production and adversely impact groundwater-dependent ecosystems. Relatively fewer studies have been conducted on climate-change impacts on groundwater resources compared to surface water systems, and the uncertainties on the recharge estimates are large. There appears to be an urgent need for including groundwater systems in climate impact assessment and in climate mitigation strategies. Moreover, feasible strategies for water resource management under such an extreme climate scenario are also required.