HELGA: a global hydro-economic model of groundwater-fed irrigation from a farmer's perspective

Overexploitation of groundwater for irrigation can ultimately threaten the viability of agriculture itself, because the falling groundwater levels become too deep to sustain the increasing costs of groundwater extraction, an economic limit is reached. In order to evaluate possible adaptation strategies to avoid or postpone reaching the economic limit, we developed the microeconomic heuristic model HELGA (hydro-economic limits as a global analysis). HELGA considers the interaction of groundwater with irrigation at the farm level with a global scale application in mind. HELGA evaluates the development of the costs and revenue of groundwater-fed irrigated agriculture from the farmer’s perspective. As long as the farm remains economically viable, the farmer can invest to access deeper groundwater, but in the long run the famer may have to adapt to keep farming profitable. We applied HELGA in five locations within the conterminous USA. In most cases, recharge is large enough to save a farmer from reaching the economic limit. Where groundwater is overexploited, the increasing energy cost of groundwater pumping is one of the main drivers limiting groundwater use. Additionally, the increasing costs of the water infrastructure (i.e. deeper wells) is a crucial factor that explains where and when the economic limit is reached. If farmers change crops wisely or fallow part of their land, they are able to access groundwater longer and postpone the moment the economic limit is reached. Using HELGA, we show that proper and timely adaptation measures increases the profitable lifetime of groundwater and helps to conserve this resource for future generations.