Temporal characteristics of pan evaporation trends under the humid conditions of northeast India
Introduction
Evaporation is an important climatic parameter that affects both plant and animal life. Pan evaporation (Epan) changes are of great significance for water resource planning, irrigation control and agricultural production. It is routinely measured by various agencies in India because of its widespread applications. Several researchers (Sarkar and Thapliyal, 1988, Thapliyal and Kulshrestha, 1991, Kothyari and Singh, 1996, Arora et al., 2005) have carried out studies on changes in rainfall and temperature around India. In contrast a little attention has been given to changes in evaporation barring one study of Chattopadhyay and Hulme (1997).
Trends in Epan have been analyzed for many regions resulting in differing conclusions. Increasing trends in Epan have been reported in Israel's central coastal plain (Cohen et al., 2002) and in northeast Brazil (da Silva, 2004). However, decreasing trends were reported by Peterson et al. (1995) and Golubev et al. (2001) in the United States and former Soviet Union, by Roderick and Farquhar (2004) in Australia, by Jun et al. (2004) in Japan, by Liu et al. (2004) in China, by Tebakari et al. (2005) in Thailand and by Burn and Hesch (2007) in Canadian Prairies.
Northeast India has great economic dependence on crops like paddy, tea and forest products. Any major changes in the water budget may have major consequences on hydrologic processes. The studies relating to the evaporation over northeast India are very important for irrigation planning. Thus, this study was carried out with the objective of studying the temporal variation of Epan on annual and seasonal basis over the humid climate of northeast India.
Section snippets
Details of study area
In this study, eleven sites (Agartala, Chuapara, Gungaram, Margherita, Nagrifarm, Nagrakata, Pasighat, Silcoorie, Thakurbari, Tocklai and Umiam) were selected (Fig. 1). Endowed with a sub tropical type of climate, the northeast region forms a distinct climatic zone within the Indian landmass with a remarkable variability of weather and climate. It is one of the heaviest rainfall regions in the world. The mean temperature over this region varies from 5 to 30 °C and the mean relative humidity
Results and discussion
In this study, the trend analysis of Epan and other meteorological parameters was carried out by Mann–Kendall and linear regression tests at 5% and 10% level of significance for eleven sites. A brief summary of results is as follows:
Conclusions
The results of this study indicate a broad general pattern of decreasing pan evaporation trends in the northeast India. Eight sites observed decreasing Epan trends in the yearly duration. However, an increasing Epan was also observed over Pasighat. Eight and nine sites showed decreasing Epan trends in the monsoon and pre monsoon seasons, respectively. Chattopadhyay and Hulme (1997) also reported Epan decreases mainly in pre monsoon and monsoon seasons. They observed decreasing Epan trends in
Acknowledgement
Authors are grateful to the agencies that provided the data used in the present study. Authors also gratefully acknowledge the helpful comments of the reviewers.
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