Drought, agricultural adaptation, and sociopolitical collapse in the Maya Lowlands

National Academy of Sciences (NAS) | May 5th, 2015

Paleoclimate records indicate a series of severe droughts was associated with societal collapse of the Classic Maya during the Terminal Classic period (∼800–9

Paleoclimate records indicate a series of severe droughts was associated with societal collapse of the Classic Maya during the Terminal Classic period (∼800–950 C.E.). Evidence for drought largely derives from the drier, less populated northern Maya Lowlands but does not explain more pronounced and earlier societal disruption in the relatively humid southern Maya Lowlands. Here we apply hydrogen and carbon isotope compositions of plant wax lipids in two lake sediment cores to assess changes in water availability and land use in both the northern and southern Maya lowlands. We show that relatively more intense drying occurred in the southern lowlands than in the northern lowlands during the Terminal Classic period, consistent with earlier and more persistent societal decline in the south. Our results also indicate a period of substantial drying in the southern Maya Lowlands from ∼200 C.E. to 500 C.E., during the Terminal Preclassic and Early Classic periods. Plant wax carbon isotope records indicate a decline in C4 plants in both lake catchments during the Early Classic period, interpreted to reflect a shift from extensive agriculture to intensive, water- conservative maize cultivation that was motivated by a drying climate. Our results imply that agricultural adaptations developed in response to earlier droughts were initially successful, but failed under the more severe droughts of the Terminal Classic period.

Droughts impede water balance recovery from fires in the Western United States

Nature Portfolio (Springer Nature) | January 2nd, 2024

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and overall ecosystem. Drought can compound the ecosystem disturbance caused by fire, although how these compound effects on hydrologic and ecosystem recovery vary among ecosystems is poorly understood. Here we use remote sensing-derived high-resolution evapotranspiration (ET) estimates from before and after 1,514 fires to show that ecoregions dominated by grasslands and shrublands are more susceptible to drought, which amplifies fire-induced ET decline and, subsequently, shifts water flux partitioning. In contrast, severely burned forests recover from fire slowly or incompletely, but are less sensitive to dry extremes. We conclude that moisture limitation caused by droughts influences the dynamics of water balance recovery in post-fire years. This finding explains why moderate to extreme droughts aggravate impacts on the water balance in non-forested vegetation, while moisture accessed by deeper roots in forests helps meet evaporative demands unless severe burns disrupt internal tree structure and deplete fuel load availability. Our results highlight the dominant control of drought on altering the resilience of vegetation to fires, with critical implications for terrestrial ecosystem stability in the face of anthropogenic climate change in the West.

Droughts in California

Public Policy Institute of California (PPIC) | April 1st, 2021

Dry Me a River: Ecological Effects of Drought in the Upper San Francisco Estuary

University of California, Davis (UC Davis) | May 24th, 2024

Dry Year Program (1978)

California State Water Resources Control Board (SWRCB) | January 1st, 1978

The importance of water was emphasized to all Californians during the 1975-76 water year. A high pressure system persisted off the West Coast for months, preventing Pacif

The importance of water was emphasized to all Californians during the 1975-76 water year. A high pressure system persisted off the West Coast for months, preventing Pacific storms from depositing moisture on major areas of the State. As a consequence, the 1975-76 period turned out to be the third driest water year in recorded State history, being surpassed only by the droughts of 1923-24 and 1930-31. With most of the State•s surface reservoirs substantial l y depleted and meager prospects for normal runoff, Governor Brown - on the last day of 1976 - announced an eight-point drought emergency program. In effect, the emergency program marshaled the resources and personnel of all state agencies in an effort to ease, as much as possible, the social and economic impact on Californians if the drought should continue for a second year . As it developed, 1976-77 became the driest year of record, amply justifying the Governor's foresight. The State Water Resources Control Board (State Board) role in the emergency program was to develop a program of water conservation in cooperation with the University of California; to determine the quantity of water which could be expected in critically dry areas; and to protect the priority of uses of that limited supply in accordance with the State's water rights law. This was particularly important in the case of agriculture, the State's No. 1 industry. It appeared likely that the available supply of water would not meet the needs of farms and orchards for the full growing season or meet the full demand of municipal and industrial users and instream needs. The State Board was concerned that water users would inadvertently interfere with the water rights of others unless forewarned of the extent of availability of water to them. In addition, the warnings would be conducive to early implementation of conservation measures. The State Board established the Dry Year Program as a function within its Division of Water Rights ( Division) . This program, designed to protect and enforce the priorities of users of surface water had four objectives : 1. To identify critical drought-impacted areas in Northern and Central California. 2. To provide information on water conservation and shortage to diverters in these areas. 3. To assure that the limited water supply available would be used in accordance with established rights. 4. To take enforcement action against violations of permit and license conditions, illegal diversions and waste or unreasonable use of water.

Dynamical and Thermodynamical Causes of Large-Scale Changes in the Hydrological Cycle over North America in Response to Global Warming

American Meteorological Society (AMS) | October 15th, 2014

The mechanisms of model-projected atmospheric moisture budget change across North America are exam- ined in simulations conducted with 22 models from phase 5 of t

The mechanisms of model-projected atmospheric moisture budget change across North America are exam- ined in simulations conducted with 22 models from phase 5 of the Coupled Model Intercomparison Project. Modern-day model budgets are validated against the European Centre for Medium-Range Weather Forecasts Interim Re-Analysis. In the winter half year transient eddies converge moisture across the continent while the mean flow wets the west from central California northward and dries the southwest. In the summer half year there is widespread mean flow moisture divergence across the west and convergence over the Great Plains that is offset by transient eddy divergence. In the winter half year the models project drying for the southwest and wetting to the north. Changes in the mean flow moisture convergence are largely responsible across the west but intensified transient eddy moisture convergence wets the northeast. In the summer half year widespread declines in precipitation minus evaporation (P 2 E) are supported by mean flow moisture divergence across the west and transient eddy divergence in the Great Plains. The changes in mean flow convergence are related to increases in specific humidity but also depend on changes in the mean flow including increased low-level divergence in the U.S. Southwest and a zonally varying wave that wets the North American west and east coasts in winter and dries the U.S. Southwest. Increased transient eddy fluxes occur even as low-level eddy activity weakens and arise from strengthened humidity gradients. A full explanation of North American hydroclimate changes will require ex- planation of mean and transient circulation changes and the coupling between the moisture and circulation fields.

Economic Analysis of the 2014 Drought for California Agriculture

University of California, Davis (UC Davis) | July 15th, 2014

California is enduring its third driest year on record as agricultural, urban and environmental demands for water are at an all-time high. This report presents an assessm

California is enduring its third driest year on record as agricultural, urban and environmental demands for water are at an all-time high. This report presents an assessment of the economic impacts of the 2014 drought on crop production, livestock and dairies using a suite of models.  This analysis extends the preliminary estimates of the Central Valley drought impacts released May 19, 2014 (Howitt et al. 2014) to include:  •Broadened coverage of the Statewide Agricultural Production Model (SWAP) to include majoragricultural areas on California's central and south coasts and inland farms of the Imperial,Coachella and Palo Verde valleys, •Updated SWAP agricultural production and economic impact estimates for the Central Valleyusing the most current data available, •Estimated Central Valley impacts if the drought persists through 2015 and 2016, includingeconomic effects and the impact of increasing groundwater depletion and pumping depths usingthe California Department of Water Resources’ (DWR) C2VSIM model, •Estimated fallowing of cropland due to drought using the SWAP model, •Estimated losses to dairies and livestock using a supply elasticity approach based on pasturelosses and feed crop prices, and •Comments on the preliminary draft from various state agencies. The study finds that the 2014 drought will result in a 6.6 million acre-foot reduction in surface water available to agriculture. This loss of surface water will be partially replaced by increasing groundwater pumping by 5 million acre-feet.  The resulting net water shortage of 1.6 million acre-feet will cause losses of $810 million in crop revenue and $203 million in dairy and other livestock value, plus additional groundwater pumping costs of $454 million. These direct costs to agriculture total $1.5 billion. The total statewide economic cost of the 2014 drought is $2.2 billion, with a total loss of 17,100 seasonal and part-time jobs. Table ES-1 summarizes the key findings of the study. 

Economic Analysis of the 2015 Drought for California Agriculture

University of California, Davis (UC Davis) | August 17th, 2015

In 2015 California agriculture is facing its fourth year of severe drought. As in 2014, irrigation districts and farmers are showing more resilience to the drough

In 2015 California agriculture is facing its fourth year of severe drought. As in 2014, irrigation districts and farmers are showing more resilience to the drought than many had anticipated. Groundwater substitution has again greatly reduced crop fallowing and job losses. Water trading and operational flexibility also have significantly reduced the costs of the drought, and preservation of the most valuable crops has helped buffer economic impacts. However, the effects of drought are unevenly distributed over regions. In some regions with limited groundwater reserves the economic and employment impacts are very severe. In others, there is an increased cost of expanded groundwater use which is partially offset by high crop prices. Just as the economic impacts of the drought have grown modestly since 2014, continuation of the drought to 2016 or beyond with similar intensity is likely to slowlyerode the state’s agricultural production and employment.

Economic Analysis of the 2016 California Drought on Agriculture

University of California, Davis (UC Davis) | August 15th, 2016

Persistent dry conditions over the past few years have put California’s irrigated agriculture under severe water stress. Improved precipitation during the win

Persistent dry conditions over the past few years have put California’s irrigated agriculture under severe water stress. Improved precipitation during the winter and spring of 2016, and favorable market conditions, among other factors, have improved prospects for agriculture in 2016. However, water supply restrictions for temperature, endangered species, and salinity management continue to challenge some farming regions. We present an analysis of the economic impact of the 2016 drought on California’s agriculture. The analysis relies on a suite of models and data to estimate responses to water scarcity. The Statewide Agricultural Production Model (SWAP, Howitt et al. 2012) is calibrated to average year water conditions and used to simulate the response of agriculture to changes in water availability. SWAP model output is linked to the IMPLAN input­output model and used to estimate changes in gross revenues, employment, and value added across all related sectors ofthe economy. The report is structured as follows. First, we summarize 2016 water supply conditions for agriculture. Next, we present the results of an economic analysis of impacts to agriculture using the SWAP model, and impacts to ancillary industries using the IMPLAN model. We conclude with a discussion of policy implications, limitations, and future analyses. Several appendices provide further details on groundwater availability and cost, land fallowing, consumptive use, livestock and dairies, employment, and regional economic impacts.

Economic consequences of optimized water management for a prolonged, severe drought in California

American Geophysical Union (AGU) | May 21st, 2010

If abrupt climate change has occurred in the past and may be more likely under human forcing, it is relevant to look at the adaptability of current infrastructure system

If abrupt climate change has occurred in the past and may be more likely under human forcing, it is relevant to look at the adaptability of current infrastructure systems to severe conditions of the recent past. Geologic evidence suggests two extreme droughts in California during the last few thousand years, each 120–200 years long, with mean annual streamflows 40%–60% of the historical mean. This study synthesized a 72-year drought with half of mean historical inflows using random sampling of historical dry years. One synthetic hydrological record is used, and sensitivity to different interpretations of the paleo record is not evaluated. Economic effects and potential adaptation of California’s water supply system in 2020 to this drought is explored using a hydro-economic optimization model. The model considers how California could respond to such an extreme drought using water trading and provides best‐case estimates of economic costs and effects on water operations and demands. Results illustrate the ability of extensive, intertied, and flexible water systems with heterogeneous water demands to respond to severe stress. The study follows a different approach to climate change impact studies, focusing on past climate changes from the paleorecord rather than downscaled general circulation model results to provide plausible hydrologic scenarios. Adaptations suggested for the sustained drought are similar for dry forms of climate warming in California and are expensive but not catastrophic for the overall economy but would impose severe burdens on the agricultural sector and environmental water uses.