Greetings from the thirsty West, where the grip of La Niña is just beginning to show signs of weakening. Up until mid March, California and much of the Western region has been experiencing below average temperature and well below average precipitation. Unlike El Niño events, where the West typically receives well above normal rainfall during the wet season, La Niña events are usually cold, but can bring either above or below average precipitation and thus greatly impact the resultant snow pack that so much of the West depends on for agriculture, industry and urban consumption.
Current sea surface temperature monitoring in the South Pacific and weather modeling agencies are predicting that we will return to neutral El Niño/Southern Oscillation conditions for the summer of 2012. Lingering effects of the gradually dissipating La Niña cycle, based on most predictions, suggest that the southern and central United States will see above average temperatures for the period through May, and the West and Northwest will see cooler than average temperatures. For the next couple of months, the northwest and northern tier states are predicted to see above average precipitation, and the Southwest will be drier than normal.
Across California, Nevada and Utah, ENSO (El Niño/Southern Oscillation) modeling suggests that we will receive normal rainfall levels, but given the near-drought conditions we have experienced so far and the fact that the “rainy season” normally tapers by mid-April, this does not bode well for our water supply. More on western precipitation patterns and potential impacts for the 2012 growing season in a moment. For anyone interested in pursuing current La Niña/El Niño/Southern Oscillation discussions, you can receive an e-mail notification from NOAA when the monthly ENSO Diagnostic Discussions are released, by sending an e-mail message to: [email protected].
As one dimension of this colder than normal winter, in Santa Cruz we have experienced 125% of our normal “chill hours” for the winter, for the 2011-12 season from November 1 through February 29. Though precise definitions vary, chill hours are commonly regarded as the total number of hours that plants are exposed to temperature between 32-45 degrees F. While chill hours are especially important for deciduous fruit tree growers, as inadequate chill can result in blind wood and delayed, erratic or staggered bloom, potentially compromising pollination, fruit set and production, flower growers also have an important stake in adequate cold exposure for our perennial crops.
Without adequate winter chill, many crops, such as roses, echinacea, forsythia, lilacs and sedum never go fully dormant. Consequently, they do not get the rest required to burst out of dormancy with big, showy blooms. Instead, during mild years, we often see continued, but weak growth throughout the winter and then light flower production during the main growing season. Fortunately, this year, both fruit and flower growers will benefit from the cold.
Researching rainfall records and snowpack information, it quickly becomes evident that in most data collection sites, we are at only 40-50% of normal for the water year to date and only 30-40% for the entire water year. Perhaps more disconcerting is the fact that in much of the West, snowpack levels in the mountains are at 30-50% of normal. This is important because much of the our water supply comes not from groundwater pumping, but rather from surface water sources: rivers and streams fed by snowmelt in the late spring and summer and the extensive reservoir system that holds back what would otherwise largely run to the ocean, for the sake of agriculture, industry and human consumption.
For early in the 2012 growing season, we may not have to worry too much because most reservoirs are in good shape. Presently, the reservoir systems of California, Nevada and Utah are all at above average levels for this time of year, due to the incredibly wet 2010-11 rain year and due to snow coming to the Sierras and other western mountains well into June. In fact, at the end of June 2011, Sierra snowpack was at 180% of normal. This, combined with a very cool summer, meant that snowmelt and runoff to the reservoirs continued through the end of summer 2011 as water demands for crop production was declining.
Arizona’s reservoirs, however, are below average for the year, and storage may continue to diminish if the Colorado River basin and the Southwest do not see at least normal precipitation for the year. As the 2010-11 water year’s dividends are used up, we will likely begin to feel the impacts our dry 2011-12 water year, in the form of water rationing, fallowed land and the desire to further exploit our precious groundwater resources.
Is groundwater pumping really the answer? Excessive pumping, defined as extracting water faster than natural recharge processes unfold, can lead to a host of long-term consequences, such as the lowering of water tables, the drying up of shallower wells, reduced stream flow and lake levels, compromised water quality, increased pumping costs, land subsidence and, for coastal communities, the disastrous advent of salt water intrusion into aquifers.
While this is certainly an issue for the arid West, groundwater depletion is a problem in regions across the country and around the world. (See the USGS image on groundwater pumping and land subsidence.) In parts of the Pacific Northwest, water tables have dropped by up to 100’. In the Ogallala aquifer, which underlies much of the Great Plains, water levels have declined by 100’ or more, though conservation, improved delivery efficiency and crop land reduction due to low commodity prices have slowed the rate of aquifer depletion. In the Arizona, water tables in the Phoenix and Tuscon areas have dropped by 300-500’, a trend unlikely to improve any time soon with continued pressure of population growth and extensive desert agriculture. Even along the around the Great Lakes, along the Gulf Coast, in Florida and the Atlantic Seaboard, drought and groundwater depletion are increasingly becoming topics of concern and examples of land subsidence are becoming all too common.
Sounds like a lot of doom and gloom. Some cynics say we should just get on with the business of using up resources and grow the economy. Manifest destiny, dominion over nature, the insatiable capitalist growth imperative and similar rhetoric are all in need of serious reexamination in light of present day phenomenon and empirical evidence that demonstrate that we are in fact living in a fragile world of finite resources and that our actions, individually and collectively, have an incredible impact on our ecosystems.
As crop producers, be it food or flowers, we have a profound responsibility to use our resources with care and respect and to be exemplars of how to live within our means. We are the consumers and stewards of Earth’s precious resources. In the realm of water, we must strive to use less by increasing soil organic matter, which like the snowpack, is a reservoir to retain soil moisture, while simultaneously improving soil structure, aeration, nutrient provisioning and facilitating more extensive root penetration.
We also need to be vigilant about the timing and methods of water delivery to avoid the drying impacts of sun and wind, watering early or late in the day depending on the presence of wind and extent of disease pressures, and by using drip irrigation and other delivery conservation strategies wherever possible. Higher density plantings, within the tolerance range of local pest and disease issues, living mulches and soil cooling surface mulching can all further contribute to water conservation. Finally, perhaps most difficult of all to ponder, is the thought that maybe we should not be growing certain water-dependent crops, or that we should be growing them only when soil moisture retention has been significantly improved, or on the margins of the rainy season when less irrigation will be needed to produce high quality crops because of natural rainfall delivery.
While there are literally hordes of resources about water in agriculture and horticulture, xeriscaping and other related topics, I thought I might leave you with the names of a few of my favorite books about water. Food for thought and contextual information to weave into our farming practices. Specifically on water in the West, I recommend Mark Reisner’s classic Cadillac Desert. Also of interest might be An Introduction to Water in California, by David Carle and California Rivers and Streams, by Jeffrey Mount. On the natural history of water and the water cycle, see Fresh Water, by E. C. Pielou and The Water Atlas, by Robin Clarke and Jannet King. Venturing into the realm of water politics and our future, see When the Rivers Run Dry, by Fred Pearce, Water Wars: Privitazation, Pollution, and Profit, by Vandana Shiva, Water, Culture and Power, by John Donahue and Barbara Rose Johnston, and finally, Water Resources: Efficient, Sustainable and Equitable Use, by Wolfram Mauser. These titles are only a very small sampling of the vast writings and thinking on water, and I have not even touched on online resources, but for anyone interested in one of our most precious resources, I hope the above works can stimulate further inquiry, reflection, activism, conservation and conversation.
To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: [email protected].
UCSC Center for Agroecology
Christof Bernau UCSC Center for Agroecology Contact at [email protected]