Opinion, Berkeley Blogs

This drought may be over, but it is bound to happen again

By Dennis Baldocchi

Figure 1 Climate at a Glance

Is the drought finally over? It must be, judging by the local resident whom I saw hosing dirt off his sidewalk on a recent rainy day.

It is true that this winter was exceedingly wet. Many regions across the state received rainfall totals that were between 150 and 200 percent of normal. So, yes, technically this drought is over. More so, if one subscribes to the official, declaration of the Governor, who pronounced an end of the "drought emergency" for most of the state.

The good news is that this excessive rain will bring succor to forests and fields following several years of extreme drought, when millions of trees died across the Sierra Nevada range. But, just because the 2016-2017 winter was wet, we can’t return to our old ways of profligate and inefficient water use.

I argue that we must abandon our old habits of wasting water. Instead, we must be wiser and treat water in California as the scarce and highly variable resource, which it is. We must use water more efficiently and sparingly. In doing so, we must also be prepared to share this resource among a set of competing, but legitimate, stakeholders like municipalities, farms, rivers, groundwater, reservoirs and natural ecosystems. We need to adopt this sparing mindset if we are to sustain our distinct California lifestyle into a warmer future, with more inhabitants, who intend to consume a cornucopia of unique, fresh, healthy and irrigated fruits, nuts and vegetables and demand fresh clean water for personal consumption.

Why must we think about water sparingly in California? We live in a Mediterranean-type climate with historically wet winters and dry summers. Another notable attribute of our semi-arid climate is that we experience much year to year variability in rainfall.

As Californians, we must be prepared to live with two types of drought. One type of drought is the one that occurs every summer, when we receive no rainfall and when evaporative demand for growing vegetation is greatest. We are able to sustain our population and agricultural economy because we have the luxury of receiving the runoff from the Sierra Nevada snowpack. This distant source supplies us with water to irrigate agricultural fields, golf courses and gardens during the summer growing season.

The other type of drought occurs every few years when we receive deficient amounts of rain during our rainy season. Our native savanna ecosystems know this fact well, as they are able to live in harmony with a variable water supply and are well adapted to survive during drought years. They have developed ecosystems with widely spaced trees, who have deep root and hardy leaves. As Californians, we’d be better prepared to allocate and distribute our water use, like the oaks, if we planned our expected water use on the basis of the amount of water available during the drier years.  Today, we suffer during the dry years because we allocate water across the state based on what is available on the average years.

To better understand the regularity of droughts, we can empower ourselves by looking at publicly available data. The NOAA site ‘Climate at a Glance’ provides a convenient tool to look at rainfall and temperature data over long time periods and for selected geographical regions. The following figure shows the time series for rainfall averaged across the state for over 100 years, through December 2016.

As we can see from the spiky lines, above and below the mean of 22.1 +/- 5.8 inches, this is a highly variable rainfall region where the year to year variability is on the order of plus/minus 26% of the mean.  A closer look at the graph reveals that we experienced 29 extreme events over the past 120 years that exceeded the standard deviation. Seventeen of those years we received less than 15 inches of rain across the state, and 12 years we have received more than 30 inches. Only once, during the drought year of 2013, did we see a year with less than 10 inches of average state-wide rainfall. Hence, it is normal that we will receive seasons and years with abundant rain fall and seasons and years with deficient rainfall.

We can’t afford to have a short attention span and think that the drought is over after a wet winter. As we can see from the historical record, drought has occurred numerous times in the past and we can count on it occurring again. We must develop water plans and water infrastructure that accommodates this reality, with the added complexity of a warming world and a growing population. We need to develop plans to share water among our diverse and legitimate stakeholders across the state. Simple solutions include installing low flow toilets, fixing leaking infrastructure, using gray water, planting water efficient gardens with native plants, and using our understanding of plant water use to schedule irrigation of crops with efficient methods, like drip irrigation rather than furrow or flood irrigation. We may need to subsidize the price of irrigation water less so the market can help readjust and help decide: 1) which irrigated crops we should be growing in a desert?; and 2) how many acres of irrigated crops we should be growing in a desert?; this prescription is less disruptive than current practices that forces farmers in certain irrigation districts to put a fraction of their land fallow, thereby causing economic hardship on them and their communities. During the wetter years, excess water should be used to refill depleted ground water reservoirs, maintain runoff for fisheries, ensure water quality, and provide wetland habitat. And, we need to think twice about all the irrigated golf courses in the desert, the amount of water they use and the price they pay for that water.

Just as our economic sensibilities drive us to ‘save our money for a rainy day’, California’s climatic realities necessitate that we bank our water for the inevitable dry periods ahead, e.g. "save our water for the dry days ahead." The impact of droughts in the future will be different as the State’s population grows, the amount of winter snowpack decreases and the evaporative demand of a warmer world increases. A warmer world will produce more rain than snow in the mountains and the runoff may come earlier.  So, the past assumption that the snow pack will provide us with ample water during the summer is not guaranteed. The capture and storage of future mountain runoff will come at a new cost associated with banking groundwater or expanding reservoirs.

In summary, droughts will occur again and their impact will be more severe in a warmer world with more evaporation. We need to be better prepared to provide future Californians, their agricultural fields, rivers and ecosystems with their fair share of that water, and not waste it on activities like hosing off the sidewalk.