Rainwater Catchment Systems under Climate Change: an Assessment of Brazilian and Japanese Cases C.O. Galvão 1, S. Oishi 2, R.L.B. Nóbrega 1 and M.S. Dantas 1 1 Department of Civil Engineering Federal University of Campina Grande Campina Grande PB 58.109-970 BRAZIL 2 Research Center for Urban Safety and Security Kobe University Kobe, 657-8501 JAPAN E-mail: galvao@dec.ufcg.edu.br Abstract: Rainwater catchment systems are today widely used worldwide for water supply and drainage systems. However, their particular purposes and uses vary according to local and regional characteristics. For instance, in Brazil and Japan, these systems are used, in urban areas, for supplementary source of water for non-potable uses. In rural areas of Brazilian semiarid region, hundreds of thousands of those systems have been built for drinking water supply, in a strategy for drought disaster mitigation. In Japan, researchers are proposing their use for eventual earthquake disaster recovery. This paper describes those cases and their particularities, as well as a simulation of their performance under present and future climate. IPCC's climate models outputs are used as input to hydraulic simulation of the rainwater catchment and storage units. The results show different performances according to the pattern of water usage in each case and also different vulnerabilities. Keywords: water management, rainfall, rainwater harvesting, climate change, IPCC. 1. INTRODUCTION Rainwater catchment systems (RWCS) are used worldwide for providing safe water for drinking and non-drinking purposes (Palmier, 2007). Usually they consist of a catchment, or harvesting, area, mostly the roofs of the buildings, a conveyance system from roof to the storage tank, filters and other sanitation devices, and a storage tank. Some of the water collected is lost within the system. Depending on the usage purpose and on the characteristics of the RWCS, a post-treatment of the water is required. Some recent efforts for assessing the impacts of climate variability and change on RWCS have been reported (eg., Galvão & Clarke, 1999; Pandey et al, 2003). As a single alternative for water supply, they have relatively high vulnerability to climate variability and change, particularly rainfall. A joint study, under way in Brazil and Japan, aims to identify rainwater usage and its vulnerability to climate variability and change in both countries. The first step is a survey of their purposes, engineering features, water demands, maintenance and management, followed by the description of rainfall pattern and variability, as well as change scenarios. This paper presents a preliminary analysis on climate change impacts on such systems in two different situations, as a basis for a wider study. 2. RAINWATER HARVESTING IN BRAZIL AND JAPAN As a first sample, two cases are being studied: the rural rainwater cisterns in the north-eastern region of Brazil and public buildings for temporarily housing people after earthquake disaster in Japan.
2.1. Brazilian Rural Semiarid In rural areas of the Brazilian semiarid region, in a strategy for drought mitigation, it is estimated that 300 000 small RWCS have been built for drinking water supply in single houses widely scattered in the region, not supplied by the conventional municipal water networks and sanitation services (Palmier & Schvartzman, 2009). They consist of a tank of 16 m 3 receiving rainwater collected from the roof of the houses, taken here as 40 m 2, with daily demand of 60 litres. Rainfall in the region is quite low in magnitude and highly variable in space and time, either at the seasonal or interannual scales. For example, at São João do Cariri (7.43 S, 36.31 W), in the period 1961-1990, annual average rainfall was 430 mm, with minimum and maximum annual values of 102 mm and 994 mm, respectively, and an annual coefficient of variation of 47% (Figure 1). Approximately 70% of this amount is concentrated between February and April. Rainfall collected during this period is further used throughout the year. The vulnerability of those systems is mainly derived from rainfall variability. 2.2. Earthquake Recovery in Japan Public spaces, such as stadiums or shopping malls are suitable to secure water for earthquake disaster recovery. For example, in the case of Yokohama area get damage from a big earthquake disaster, people, especially poorer people, would be evacuated to the stadium and stay at those installations for several days during waiting for temporary houses provided by local governments. Nissan Stadium, taken to illustrate this analysis, has a catchment area of 164 054 m 2, storage capacity of 3300 m 3 and demand estimated in 39 m 3 /day. At Yokohama (35.56 N, 139.64 E), in the period 1961-1990, annual average rainfall was 1569 mm, with minimum and maximum annual values of 995 mm and 2252 mm, respectively, and an annual coefficient of variation of 17% (Figure 2). The vulnerability of those systems is mainly derived from the demands during disaster shelter usage. Figure 1 Monthly rainfall (mm) distribution for 1961-90 in São João do Cariri, Brazil.
Figure 2 Monthly rainfall (mm) distribution for 1961-90 in Yokohama, Japan. 3. SIMULATING CLIMATE CHANGE IMPACTS A very simple approach was used to simulate climate change impacts on those systems, through a hydraulic water balance model having as input daily rainfall series representing present and future climate, generating a vulnerability index, which expresses the average percentage of days not attended by the system (Galvão et al, 2009). A set of ten years of daily rainfall was generated by a stochastic algorithm (Oliveira, 2003), both for present and future climate, using rainfall time series for 1961-90 and rainfall anomalies for 19 IPCC s climate models, for year 2100 (IPCC, 2008a,b). 4. RESULTS Daily rainfall anomalies projected by the 19 IPCC-climate models are shown in Figures 3 and 4 for São João do Cariri and Yokohama, respectively. The scenarios show that greater change is expected to happen in Yokohama than in Cariri. However, in Cariri, in average the anomalies are mostly negative. Figures 5 and 6 show the resulting monthly averages for both sites, produced by the rainfall generator, corresponding to the present (1961-90) and for a future climate (2100). These present and projected behaviors of the rainfall patterns, associated to the characteristics of the RWCS, are reflected in the estimates of the vulnerability index for both sites, expressed as the average percentage of days when water demands are not supplied (Tables 1 and 2). In Cariri, the high variability and lower amounts of rainfall, associated to high demands compared to the storage, lead to high vulnerability, either under present or future climate (Table 1). The changes in mean and median values of the vulnerability are not so high under the future scenario of Figure 3. The reason is possibly that the negative anomalies are projected for the rainiest months, with lower impact on the results due to the small tank storage, which spills often during February-April. On the other side, positive anomalies are projected for the last months of the rainy season (May June), leading to some more days when the demand is attended. As for Yokohama, some of the positive anomalies in rainfall projected for 2100 are not reflected in reducing the already low vulnerability (Table 2). The few critical events that, under present climate, cause the failures in the water supply are more frequent in the future, leading to an increase in vulnerability extremes.
Figure 3 Rainfall daily anomalies (mm) for IPCC s 2100-Scenario for São João do Cariri, Brazil. Figure 4 Rainfall daily anomalies (mm) for IPCC s 2100-Scenario for Yokohama, Japan. Figure 5 Monthly rainfall (mm) projections for 1961-90 and 2100, São João do Cariri, Brazil.
Figure 6 Monthly rainfall (mm) projections for 1961-90 and 2100, Yokohama, Japan. Table 1 Vulnerability of RWCS (%) for São João do Cariri, Brazil. Vulnerability Present Future Maximum 67.1 82.7 Minimum 4.9 0.3 Mean 35.8 40.6 Median 37.3 41.6 Table 2 Vulnerability of RWCS (%) for Yokohama, Japan. Vulnerability Present Future Maximum 3.8 10.7 Minimum 0.3 0.0 Mean 1.6 2.2 Median 1.0 1.5 5. CONCLUSIONS This exploratory and preliminary study used a standard methodology to explore future scenarios of climate change into estimates of impacts relevant to water management. IPCC s scenarios explored in the study provide only variations over monthly mean values of rainfall. Changes in variability were obtained through a stochastic rainfall generator, using present climate variability as reference. This approach certainly introduces relevant uncertainty in the projected impacts of climate change. Rainwater catchment systems are very important for Brazil and Japan, since significant water supply is done using such technologies. The results for the two case studies show that the vulnerability of those catchment systems would slightly increase in the future. These results, considering the involved uncertainties, are not conclusive. Further studies should use improved climate scenarios, which bring information not only on changes in means but also on variability, and a bigger sample of cases to characterize a regional assessment. 6. ACKNOWLEDGMENTS This work was produced under INCT-Clima and SegHidro Projects, funded by CNPq, CAPES and MCT, Brazil.
7. REFERENCES Galvão, C.O. and Clarke, R.T. (1999), Potential Benefits of Tropical Seasonal Rainfall Forecasting for Rainwater Catchment Systems, in Proceedings of the 9th International Rainwater Catchment Systems Conference. Petrolina, 1999, pp. 1-6. Galvão, C.O., Nóbrega, R.L.B., Brasileiro, F.V. and Araújo, E.C. (2009), An e-science Platform for Collaborative Generation of Knowledge and Technology in Hydrology, Hydrogeology and Water Resources, IAHS-AISH Publication, 331, 500-504. IPCC (2008a), The IPCC Data Distribution Centre. IPCC, WMO, UNEP. Available at www.ipcc-data.org. IPCC (2008b), Weather generators. IPCC, WMO, UNEP. Available at www.ipcc-data.org/ ddc_weather_generators.html. Oliveira, V.P.S. (2003) Modelo para geração de séries sintéticas de precipitação. Universidade Federal de Viçosa, Brazil, PhD Dissertation. Palmier, L.R. (2007), State of the Art of Rainwater Harvesting in Developing Countries, in Proceedings of the 11th International Conference on Diffuse Pollution, Belo Horizonte, 2007. Palmier, L.R. and Schvartzman, A. (2009), A Management and Operational Plan for Improving Cisterns Efficiency in Brazil, in Proccedings of the 14th International Rainwater Catchment Systems Conference, Kuala Lumpur, 2009. Pandey, D.N., Gupta, A.K. and Anderson, D.M. (2003), Rainwater Harvesting as an Adaptation to Climate Change, Current Science, 85 (1).