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Spatiotemporal variation and abrupt changes of potential evapotranspiration in the Wei River basin

5 th International Symposium on Integrated Water Resources Management 3 rd International Symposium on Methodology in Hydrology. Spatiotemporal variation and abrupt changes of potential evapotranspiration in the Wei River basin. College of Water Sciences, Beijing Normal University.

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Spatiotemporal variation and abrupt changes of potential evapotranspiration in the Wei River basin

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  1. 5th International Symposium on Integrated Water Resources Management 3rd International Symposium on Methodology in Hydrology Spatiotemporal variation and abrupt changes of potential evapotranspiration in the Wei River basin College of Water Sciences, Beijing Normal University Zuo Depeng, Xu Zongxue, Liu Xingcai, Cheng Lei zongxuexu@vip.sina.com

  2. Outline • 1 Introduction • 2 Data and Methodology Description • 3 Results Analysis • 4 Discussion and Conclusion

  3. 1. Introduction Evapotranspiration is the most important climatic element, a principal component of hydrological cycle, and a key input to hydrological models.

  4. 1. Introduction Understanding of the spatial distribution and temporal trend of evapotranspiration: • Great significance for water resources planning and management; • Important to improve the utilization of agricultural water resources; • Helpful to understand the spatiotemporal variation of ecological water requirements, etc.

  5. 1. Introduction • Thomas (2000) analyzed Penman-Monteith ET estimates in China and found it had decreased in all seasons during 1954-1993. • Mo et al. (2004) simulated the temporal and spatial variation of ET and analyzed its annual and seasonal variation from 1984 to 1997 in the Lushi basin. • Xu et al. (2006) examined the spatial distributions and temporal variations of reference ET, pan evaporation and pan coefficient, and discussed the causes for the variations in the Yangtze River Basin.

  6. 1. Introduction • Tong et al. (2007) analyzed the temporal and spatial variation of spring wheat ET in the Shiyang River basin in the last 50 years. • Zhang et al. (2009) calculated RETacross the Qinghai-Tibetan Plateau between 1971 and 2004, and determine the contributions of climate factors to RET change. • Liang et al. (2010) analyzed the growing season and annual ET0in the Taoer River basin during 1961-2005. • ……

  7. 1. Introduction • The Wei River plays an important role in the Yellow River management and development, and has a great strategic significance in the development of West China and regional economy. • Study on the impact of climate change in the Wei River basin has important significance in protecting and improving the ecosystem health in West China.

  8. Outline • 1 Introduction • 2 Data and Methodology Description • 3 Results Analysis • 4 Discussion and Conclusion

  9. 2.1Study area and data description • The largest tributary of the Yellow River • Daily mean, maximum and minimum air temperature, air pressure, relative humidity, wind speed and sunshine duration data at 21 meteorological stations during 1959-2008

  10. 2.1Study area and data description

  11. 2.2 Methodology description • FAO Penman-Monteith method for PET • Spline method for interpolation • Non-parametric Mann-Kendall test for monotonic trend • Non-parametric Pettitt test for abrupt change

  12. Outline • 1 Introduction • 2 Data and Methodology Description • 3 Results Analysis • 4 Discussion and Conclusion

  13. 3.1 Spatial distribution of mean annual PET • The lowest value was found in the headwater of the basin, while the highest value took place at Tongchuan in the lower reaches. • High values in east and north, low values in west and south, and decreasing from northeast to southwest.

  14. 3.1 Spatial distribution of mean seasonal PET In spring (MAM), spatial distribution was generally accordance with the annual map In summer (JJA), greatest values shifted to the south bank of the lower Wei River Mean seasonal PET were in the order of summer > spring > autumn > winter, accounting for 31%, 41%, 18% and 10% of mean annual value, respectively In autumn (SON), the smallest values were found in the headwater while the greatest values took place at the outlet of the watershed In winter (DJF), spatial distribution was generally accordance with the autumn map

  15. 3.2 Temporal trend for annual PET series • 15 stations which uniformly distributed in the basin showed increasing trend, 6 of which were detected as statistically significant increasing trend. • 6 stations which located in the middle-lower reaches region showed decreasing trend, 3 of which around Xi’an City were detected as statistically significant decreasing trend.

  16. 3.2 Temporal trend for seasonal PET series In summer (JJA), the upper reaches region showed increasing trend, while decreasing trend took place at most part of the middle-lower reaches region Spring (MAM) had overall increasing trend, 8 of which were significant More than 70% of the total stations showed increasing trend in Autumn (SON), and only 6 middle-lower reaches stations decreased Winter PET (DJF) showed increasing trend at 10 stations which mostly located in the upper-middle reaches region

  17. 3.3 Abrupt change of annual PET series • One abrupt change appeared in 1993 for annual PET at significance level of 5%. • Annual mean air temperature and relative humidity were also detected as significant abrupt change in 1993. This may indicate that the two meteorological variables are the main cause of change in PET.

  18. 3.3 Abrupt change of seasonal PET series Abrupt change of summer PET took place in 1975, consequently, a significant increase appeared after the detected abrupt change Abrupt change of spring PET series occurred in 1993 too, and the test statistics regime of spring PET was generally accordance with that of annual PET There was no statistically abrupt change in autumn and winter

  19. Outline • 1 Introduction • 2 Data and Methodology Description • 3 Results Analysis • 4 Discussion and Conclusion

  20. 4. Discussion and Conclusion • Spatial distribution of mean annual PET in the WRB was generally characterized with high values in east and north, low values in west and south, decreasing from northeast to southwest. • Mean seasonal PET were in the order of summer > spring > autumn > winter. • Annual PET series at most part of WRB showed increasing trend. • One significant abrupt change appeared in 1993 for annual PET.

  21. 4. Discussion and Conclusion • Further attention should be paid to the contributions of key climatic variables to the change of PET, such as air temperature, solar radiation, relative humidity and wind speed. • Therefore, the study on sensitivity of PET to key climatic variables using the sensitivity coefficients method is undergoing. And the preliminary result shows that relative humidity is probably the most sensitive variable.

  22. Thanks for your attention!

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