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Impacts of climate variability on reference evapotranspiration over 58 years in the Haihe river basin of north China

Author:
Tang, Bo, Tong, Ling, Kang, Shaozhong, Zhang, Lu
Source:
Agricultural water management 2011 v.98 no.10 pp. 1660-1670
ISSN:
0378-3774
Subject:
Food and Agriculture Organization, air temperature, climate, climate change, evapotranspiration, vapor pressure, watersheds, wind speed, China
Abstract:
Physically, evaporative demand is driven by net radiation (Rₙ), vapour pressure (eₐ), wind speed (u₂), and air temperature (Tₐ), each of which changes over time. By analyzing temporal variations in reference evapotranspiration (ET₀), improved understanding of the impacts of climate change on hydrological processes can be obtained. In this study, variations in ET₀ over 58 years (1950–2007) at 34 stations in the Haihe river basin of China were analyzed. ET₀ was calculated by the FAO Penman–Monteith formula. Calculation of Kendall rank coefficient was done by analyzing the annual and seasonal trends in ET₀ derived from its dependent climate variables. Inverse distance weighting (IDW) was used to analyze the spatial variation in annual and seasonal ET₀, and in each climate variable. An attribution analysis was performed to quantify the contribution of each input variable to ET₀ variation. The results showed that ET₀ gradually decreased in the whole basin over the 58 years at a rate of −1.0mmyr⁻², at the same time, Rₙ, u₂ and precipitation also decreased. Changes in ET₀ were attributed to the variations in net radiation (−0.9mmyr⁻²), vapour pressure (−0.5mmyr⁻²), wind speed (−1.3mmyr⁻²) and air temperature (1.7mmyr⁻²). Looking at all data on a month by month basis, we found that Tₐ had a positive effect on dET₀/dt (the derivative of reference evapotranspiration to time) and Rₙ and u₂ had negative effects on dET₀/dt. While changes in air temperature were found to produce a large increase in dET₀/dt, changes in other key variables each reduced rates, resulting in an overall negative trend in dET₀/dt.
Agid:
530274