Climate risk management for water in semi–arid regions

Background: New sources of hydroclimate information based on forecast models and observational data have the potential to greatly improve the management of water resources in semi-arid regions prone to drought. Better management of climate-related risks and opportunities requires both new methods to develop forecasts of drought indicators and river flow, as well as better strategies to incorporate these forecasts into drought, river or reservoir management systems. In each case the existing institutional and policy context is key, making a collaborative approach involving stakeholders essential. Methods: This paper describes work done at the IRI over the past decade to develop statistical hydrologic forecast and water allocation models for the semi arid regions of NE Brazil (the “Nordeste”) and central northern Chile based on seasonal climate forecasts. Results: In both locations, downscaled precipitation forecasts based on lagged SST predictors or GCM precipitation forecasts exhibit quite high skill. Spring-summer melt flow in Chile is shown to be highly predictable based on estimates of previous winter precipitation, and moderately predictable up to 6 months in advance using climate forecasts. Retrospective streamflow forecasts here are quite effective in predicting reductions in water rights during dry years. For the multi-use Oros reservoir in NE Brazil, streamflow forecasts have the most potential to optimize water allocations during multi-year low-flow periods, while the potential is higher for smaller reservoirs, relative to demand. Conclusions: This work demonstrates the potential value of seasonal climate forecasting as an integral part of drought early warning and for water allocation decision support systems in semi-arid regions. As human demands for water rise over time this potential is certain to rise in the future. Background Water scarcity in semi-arid regions having only one rainy season per year is a serious problem especially in developing countries. Seasonal climate forecasts, where they are skillful, provide a potential mechanism tomanage drought in rainfed areas, and to better manage water allocation and reservoir operations. This paper describes approaches developed at the IRI in two semi-arid regions of South America, Central Chile, and NE Brazil covering these three aspects. *Correspondence: [email protected] 1International Research Institute for Climate and Society, The Earth Institute, Columbia University, Palisades, New York, USA Full list of author information is available at the end of the article The central Chile case study Climate variability can have serious social impacts in semiarid regions, especially for farmers who depend on rain-fed agriculture and on livestock production based on natural vegetation. In the Elqui Valley and Coquimbo region in central northern Chile (approx. 28S–32S), where rainfall amounts often drop under the limit for crop growth, a lack of rainfall results in a crisis situation for society. Over USD2.6 million were spent during the severe drought of 2007 to support affected families and farmers as they repair damage, recover degraded soils, and increase irrigation programs (MINAGRI 2008). A typical problem here is the lack of preparedness prior to these natural events, making any governmental action afterward less cost effective. Despite the need, the current Drought Alleviation Plan formulated by the Chilean government for the region (FOSIS 2008) does not include © 2014 Robertson et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Robertson et al. Earth Perspectives 2014, 1:12 Page 2 of 13 http://www.earth-perspectives.com/content/1/1/12 strategies for drought early warning, and the feasibility of such a system has yet to be demonstrated. The majority of precipitation in the region falls during the austral winter (May–August) as rain in the Valley and snow in the mountains, leaving the remaining months extremely dry (Aceituno 1988; Carrasco et al. 2008). Total precipitation averages approximately 100 mm annually near the coast, with larger amounts towards the Cordillera and south, and with a high degree of interannual variability (Young et al. 2010). El Niño-Southern Oscillation (ENSO) has been identified as a strong driver of this variability, with positive precipitation anomalies during El Niño events and below normal precipitation mostly associated with La Niña conditions (Aceituno 1988; Montecinos and Aceituno 2003; Falvey and Garreaud 2007; Garreaud et al. 2009; Quintana and Aceituno 2012). The Elqui River is predominantly fed through snowmelt over the October–January season, and a skillful streamflow forecast could provide advanced information to guide water allocation decisions in the Valley, especially during drought. During the 1980s and 1990s, the framework for privatized water in Chile was established to encourage optimal allocation and efficiency through a market-oriented approach, as prescribed by the Water Code of 1981 (Donoso 2006; Young et al. 2010). The national water authority initially issued water rights, while supervision is the responsibility of the local water authority. Rights along the Elqui River are fully allocated, with each right valued at 1 liter per second. In years with near normal or above normal precipitation and snowpack in the Andes, supply is typically sufficient for all holders to use the full 1 liter per second; however in years with less than normal precipitation and snowpack, a reduction in the water rights value is required, occasionally to 0.5 liters per second or even less. All water rights holders have equal priority. Farmers dominate the landscape, holding approximately 92% of all rights, with half of those held by a small minority practicing large-scale viticulture. Municipalities and the mining industry share the remaining rights. Skillful forecasts of potential water rights reductions may thus be informative for planning purposes across a number of sectors. The Nordeste case study Northeast Brazil is a region with a high potential for seasonal rainfall predictability during the February–April rainy season, due to strong teleconnections with ENSO and with variability of the tropical Atlantic Ocean (Hastenrath and Heller 1977; Moura and Shukla 1981; Nobre and Shukla 1996). Reservoir optimization results are shown for the Oros system, which is the upper most reservoir in the Jaguaribe-Metropolitan multi-reservoir system. Currently, a conservative policy is used in water allocation for municipal, industrial, and agricultural use, assuming zero inflow into the reservoir in the upcoming year—essentially assuming a drought will occur every year. The work reviewed here investigates the potential for climate forecasts to improve the water allocation and reservoir releases through pre-emptive optimization analyses that are used to guide subsequent land use and other water sensitive decisions in a collaborative setting.