It feels weird to write about water scarcity during this very wet, rainy season. However, streamflows throughout the Nooksack River basin are very low during the summer, when fish most need abundant cold, clean water.
Agricultural irrigation is the largest water user in Whatcom County. And its use peaks during the summer months. Because irrigation is so important to water quantity and quality, we need to know how much water farmers use, for which crops and when. Unfortunately, no data exists in the public domain on actual water use, i.e., water-meter data. Instead, we have various estimates, which vary widely (see Figure).
Recently, “a new online platform that uses satellites to estimate water used by crops ...” has become available. This system estimates crop evapotranspiration (ET) for individual fields, along with the crop type and field size, from January 2016 to the present. (ET is the sum of plant transpiration, evaporation from the soil surface, and water used for plant growth.)
These new estimates suggest that irrigation of 46,000 acres of Whatcom farmland uses about 70,000 acre-feet of water a year, equivalent to 1.5 acre-feet/acre. Water use varies from year to year (from almost 60,000 to 90,000 acre-feet/year), depending on rainfall, air temperatures and other factors. Irrigation water use varies substantially from month to month, with water use greatest in June, July and August.
These new data, as well as other estimation methods, are helpful but not sufficient for understanding the details of agricultural water use. Specifically, water-meter data are necessary to:
- understand how irrigators can and should prepare for and respond to droughts and the near-certain effects of climate change,
- assess the costs and benefits of higher-efficiency irrigation equipment,
- assess the costs and benefits of improved maintenance and scheduling practices, and
- compare the costs and benefits of new supply, storage, and water-use efficiency projects.
Climate change is an especially serious threat because it will both reduce the amounts of water available in the summer (glacier shrinkage, less snow and more rain in the winter, earlier snowmelt) and increase the amounts of water needed for irrigation (hotter, dryer summers).
Editor note: The full PDF of Eric's paper is linked just below.