While nearly all of the most costly 2017 weather/climate events involved excessive water, droughts can be as consequential. The causes of drought vary by location, research continues to untangle the complex causes: climate variability and ocean temperatures, interactions between the land and the atmosphere, human alterations of land/vegetation/water cycle, climate change, and many other factors.
Droughts are natural events influenced by human activities. Evidence of mega-droughts in the southwest US indicate they have and will continue to occur infrequently. Yet the 1930s dust bowl was exacerbated by agriculture and top soil removal. Droughts limit productivity of rain fed crops and can depleted water stores from irrigation (water removed but not replenished)
Drought reduces corn output (Zippeet al 2016 Environ. Res. Lett.)
The US states that rely most heavily on irrigation are located in the Southwest. Irrigated agriculture enables crop production in these arid regions, however droughts are frequent. Increasing water use cannot continue; groundwater stores are declining. Climate change is expected to exacerbate the issue although the science cannot produce the local scale information farmers would benefit from.
Groundwater depletion between 1900 and 2008 (USGS).
So irrigation is needed during droughts to prevent crop losses as well as enable agriculture in arid regions that never receive the needed rainfall. Globally, depletion of water stores, specifically groundwater (largest non-ice fresh water store globally). Water must be sustainably consumed, founded on more efficient agricultural use.
Groundwater depletion between 1900 and 2008 (USGS).
Possible futures
Future changes in drought and water use due to changes in climate from anthropogenic greenhouse gas emissions remains uncertain. Higher temperatures cause increased evaporation of soil water, heat stress (heatwaves) can kill crops, changes in precipitation are uncertain, increased CO2 concentrations may reduce amount of water crops use, and the frequency and magnitude of future droughts remains a mystery.
Despite the many uncertainties, possible future changes in agriculture due to changes in climate have been produced.
The figure above is only a possible outcome, derived from a single climate model (not robust). It does highlight the fundamental roles weather, climate, humans,land-atmosphere coupling, and hydrology all have in shaping water resources, food production and agriculture.
My research is one part of a global effort to advance the science of water, weather, and climate. Ultimately the goal is processes level understanding and predictive modeling systems; be it forecasting next weeks flood or the probability of a severe drought in the coming decade.
Irrigation projections commonly use land only models (red points), neglecting land-atmosphere coupling, we showed that land-atmosphere feedbacks (blue) significantly change irrigation estimates. Land-atmo coupling moistens the near surface air (left panel), causing lower mean irrigation rates with increased variability (right panel).
