Nonsustainable groundwater sustaining irrigation: A global assessment

TLDR

Irrigated crops rely on green water from local precipitation, blue water from surface and renewable groundwater, and nonrenewable groundwater abstracted from nonlocal sources. This study quantifies the global share of nonrenewable groundwater used to sustain current irrigation practices. Using the PCR‑GLOBWB global hydrological model, the authors simulated crop water demand and available blue/green water, downscaled country groundwater abstraction statistics, and compared these with simulated recharge and irrigation return flow to estimate nonrenewable abstraction. Nonrenewable groundwater accounted for about 20 % of global irrigation demand in 2000, with India, Pakistan, the United States, Iran, China, Mexico, and Saudi Arabia contributing the largest shares, and the global contribution rising from 75 to 234 km³ yr⁻¹ between 1960 and 2000.

Abstract

Water used by irrigated crops is obtained from three sources: local precipitation contributing to soil moisture available for root water uptake (i.e., green water), irrigation water taken from rivers, lakes, reservoirs, wetlands, and renewable groundwater (i.e., blue water), and irrigation water abstracted from nonrenewable groundwater and nonlocal water resources. Here we quantify globally the amount of nonrenewable or nonsustainable groundwater abstraction to sustain current irrigation practice. We use the global hydrological model PCR‐GLOBWB to simulate gross crop water demand for irrigated crops and available blue and green water to meet this demand. We downscale country statistics of groundwater abstraction by considering the part of net total water demand that cannot be met by surface freshwater. We subsequently confront these with simulated groundwater recharge, including return flow from irrigation to estimate nonrenewable groundwater abstraction. Results show that nonrenewable groundwater abstraction contributes approximately 20% to the global gross irrigation water demand for the year 2000. The contribution of nonrenewable groundwater abstraction to irrigation is largest in India (68 km 3 yr −1 ) followed by Pakistan (35 km 3 yr −1 ), the United States (30 km 3 yr −1 ), Iran (20 km 3 yr −1 ), China (20 km 3 yr −1 ), Mexico (10 km 3 yr −1 ), and Saudi Arabia (10 km 3 yr −1 ). Results also show that globally, this contribution more than tripled from 75 to 234 km 3 yr −1 over the period 1960–2000.