The Long Game: Defining Drought and Its End
What do we mean when we say drought? And more complicated still, what do we mean when we say drought is over? These questions consumed much public attention in California as the first few weeks of January 2017 brought quenching, if somewhat destructive, storms to northern parts of the state. Since the start of this water year on October 1st 2016, it has been reported that precipitation in the northern Sierra is 218% of average (January 11th); downtown LA had gotten 8.8 inches of rain, or 167% of average; that rivers like the Russian River (Sonoma and Mendocino counties) and the Yuba River (Nevada County) were overflowing; that the Sierra Nevada snowpack was at 163% its average level for this time of year (January 13th); that the Oroville Reservoir is at 80% of total capacity and 125% of its historical average (January 16th); and that 42% of the state was "out of drought" (January 12th).
Alas, there is no consensus on the definition of the word drought or the concept of its end, and therefore we may not all be hearing the same meaning in either of the two. The public sentiment that a wet start to 2017 means the five-year drought is over could lead to prematurely abandoning conservation behavior and policy. Therefore, in this moment where the status of the state's water resources is shifting, it is important to define the metrics by which we measure drought before making claims that it has come to an end. It is clear from the reports and articles above that the understanding of drought is some combination of a lack of water falling from the sky, water running through the land, and water stored below ground. One way to organize these indicators of drought (or its end) is according to the timing of their impact.
The United States Drought Monitor (USDM) is one classification scheme cited by multiple articles claiming an end to the drought. This national tool defines the extent of drought according to five categories, D0-D4, in order of escalating severity. The USDM uses five main indices and models to determine its categorizations: The Palmer Drought Severity Index (based on precipitation, temperature, and water-holding capacity of soil), the CPC Soil Moisture Model (based on precipitation, temperature, soil moisture, evaporation and run-off), USGS Weekly Streamflow (based on continuously functioning measuring device that computes daily average streamflow and quality), Standardized Precipitation Index (based on time series precipitation data), and Objective Drought Indicator Blends (based on precipitation, approximates drought related impacts). The USDM recognizes some of the shortcomings of these indicators, like their limited ability to factor in the impact of winter snows, and the lack of accounting for groundwater levels, reservoir storage and pasture/range conditions. The USDM adds these measurements into their drought severity calculations as well local observations and expert judgments to create a more complete picture.
That said, even such a detailed tool as the USDM that takes into account all of the indicators in the schematic above, can only speak to drought conditions of a locality in isolation, not as a part of a regional system. In Peter Gleik's article, "Is the drought over? Wrong question!" he argues that looking at indicators like precipitation, snowpack, reservoirs, aquifers, and even forest and fish health and agricultural deliveries are not sufficient to look at in isolation. Instead, he argues that we should be asking, "are we managing our water in a sustainable way?" To which his answer is still no. The question, is California's drought over is particularly difficult to answer because its rivers and man-made pipelines and aqueducts not only connect the water-rich north to the water-poor south, they also connect California to neighboring states and to Mexico. Therefore, for a measure of drought to accurately predict the state's ability to meet current and future human and environmental needs, it would need to account for man-made water diversions locally and regionally.
To this end, the State and local governments should be moving ahead with financial tools and public instruments that encourage reduced consumption, reuse of water resources, and development of new, sustainable water resources. We should be following through investments in new technologies and business models that make the water sector in California and other drought-stricken regions environmentally sustainable, as described in the Milken Innovation Center’s Financial Innovations Lab in 2016, “Financial Models for Water Sustainability.” And we should be remediating and better managing our eco-system of natural water sources, including rivers, reservoirs, and aquifers. In the meantime, it seems reasonable to have gratitude for the increased water budget from this month's rain and stay focused on maintaining and improving the sustainability of our personal and public water management practices.