Assessment of vineyard water use for irrigation and frost protection in two watersheds in Northern California (USA)

Abstract

In California, surface water is a public trust resource that is used by competing interests including urban, agriculture, fish and wild life and other needs. We evaluated vineyard water use on a landscape scale in two watersheds in a climate where 95% of precipitation occurs between November and May. The Upper Russian River Watershed has two large on-stream reservoirs that enable regulated water flow year round. The Navarro River Watershed is a wild river with no on stream storage, and in stream flow is dependent strictly on annual precipitation. Precipitation and flow rates in both watersheds are highly variable from year to year. Both rivers are habitat to endangered salmonid fish. Vineyard water use for frost protection and irrigation occurs from April to October when river flow rates are at their lowest and juvenile fish can be stranded and killed by dewatering. In our studies, we used GIS information to delineate and show spatially where vineyards are located in the watersheds. We also reviewed data from stream flow gauges to identify the time of lowest flows and compare that with vineyard water use. We reviewed public and private historic weather station evapotranspiration data to develop reference evapotranspiration (ETo) for most vineyard regions in the study area. We also sampled 73 vineyard blocks to determine vineyard canopy size to estimate average crop coefficients (ETc) for both watersheds. At the same time, we evaluated vineyard drip irrigation systems to determine distribution uniformity. We surveyed a representative sample of growers on their irrigation and frost protection practices to determine the actual amount of water that they used during the years of our studies (2007 and 2009). In this way, we were able to develop vineyard water budgets for both watersheds. We also determined where most growers source their water for frost protection and irrigation including direct surface diversion from the rivers, off stream ponds or wells. We found that the two watersheds were different in water use due to both climate, in stream water flow and sources of water. In the Navarro River Watershed, there are 1116 ha of vineyard that use approximately 1524 megaliters per year for irrigation and frost protection purposes. In the Russian River watershed, there are 4,4991 that require 15, 284 megaliters. Most vineyard irrigation systems are very efficient, with an average distribution uniformity > 89%. These studies are a helpful planning tool to better understand water use by vineyards over a large area and their impact on available water resources.