Abstract
Pan evaporation (Epan) is an important indicator of regional evaporation intensity and degree of drought. However, although more evaporation is expected under rising temperatures, the reverse trend has been observed in many parts of the world, known as the “pan evaporation paradox”. In this paper, the Haihe River Basin (HRB) is divided into six sub-regions using the Canopy and k-means (The process for partitioning an N-dimensional population into k sets on the basis of a sample is called “k-means”) to cluster 44 meteorological stations in the area. The interannual and seasonal trends and the significance of eight meteorological indicators, including average temperature, maximum temperature, minimum temperature, precipitation, relative humidity, sunshine duration, wind speed, and Epan, were analyzed for 1961 to 2010 using the trend-free pre-whitening Mann-Kendall (TFPW-MK) test. Then, the correlation between meteorological elements and Epan was analyzed using the Spearman correlation coefficient. Results show that the average temperature, maximum temperature, and minimum temperature of the HRB increased, while precipitation, relative humidity, sunshine duration, wind speed and Epan exhibited a downward trend. The minimum temperature rose 2 and 1.5 times faster than the maximum temperature and average temperature, respectively. A significant reduction in sunshine duration was found to be the primary factor in the Epan decrease, while declining wind speed was the secondary factor.
Highlights
IntroductionTemperature records indicate that the earth has warmed by approximately 0.6 ◦ C during the 20th century [2]
Global warming has become an indisputable fact [1]
As a key component in the hydrological cycle, evapotranspiration is associated with water balance and water exchange, as well as surface energy balance; of all components of the water cycle, evapotranspiration is the factor most directly affected by climate change [6]
Summary
Temperature records indicate that the earth has warmed by approximately 0.6 ◦ C during the 20th century [2]. This increase in global temperature has significantly impacted the natural environment, ecosystem, and social economy [3], and has led to a series of changes in hydrological factors, such as precipitation, evaporation, water infiltration, soil moisture, river runoff, and groundwater flow, all of which affect the global hydrological cycle. As a key component in the hydrological cycle, evapotranspiration is associated with water balance and water exchange, as well as surface energy balance; of all components of the water cycle, evapotranspiration is the factor most directly affected by climate change [6]. Analyzing the climate sensitivity of evapotranspiration has important theoretical and practical implications for understanding the impact of climate change on the hydrological cycle [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
