NHESSD Natural Hazards and Earth System Sciences Discussions NHESSD Nat. Hazards Earth Syst. Sci. Discuss. 2195-9269 Göttingen, Germany 10.5194/nhess-2018-305 Research on Occurrence and Development of Pasture Drought Events in Alpine Grassland using the Drought Threshold Zhang Tiaofeng 1 2 Li Lin 3 Xiao Hongbin 4 Li Hongmei 1 Qinghai Climate Center, Xining, 810000, PR China College of Atmospheric Science, Lanzhou University, Lanzhou, 730000, PR China Weather Modification Office of Qinghai Province, Xining, 810000, PR China Qinghai Institute of Meteorological Science, Xining, 810000, PR China 17 12 2018 2018 1 18 Copyright: © 2018 Tiaofeng Zhang et al. 2018 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://nhess.copernicus.org/preprints/nhess-2018-305/ The full text article is available as a PDF file from https://nhess.copernicus.org/preprints/nhess-2018-305/nhess-2018-305.pdf

Pasture is vital to livestock husbandry development in Qinghai and even in North China. Drought is the primary meteorological disaster that affects pasture, but insufficient soil moisture is the most prominent cause of pasture drought. Timely and accurate determination of the soil moisture threshold of pasture is important for objective recognition and monitoring of the occurrence and development of pasture drought. This study aims at investigating pasture responses to soil drought as well as quantitative expression of soil drought degree and drought threshold. Test plots were selected from the pasture test station. Five testing groups were set according to coverage rate (0&ndash;100&thinsp;%) at the initiation the pasture growth period. The impacts of profile moisture characteristics, drought threshold, and precipitation on duration of pasture drought were studied. Research results have demonstrated that moisture in the soil profile below 20&thinsp;cm decreases slightly throughout drought events in alpine grassland. Changes of soil moisture in the 0&ndash;20&thinsp;cm layer can generally reflect drought stress of the pasture. In the process of a drought event, the relationship between soil water storage and cumulative relative water loss can be expressed via a logarithmic linear equation. Quantitative expression of drought degree in grasslands can be realized by transforming the slope of this equation into the index <i>D</i> with an interval of [0, 1]. The occurrence rates of mild drought,moderate drought, and severe drought were 0.36, 0.45, and 0.70, respectively. The duration of severe drought was closely related with initial soil moisture. The relationship between duration of drought and the necessary minimum precipitation can be expressed by an exponential equation. Values of the <i>D</i> index can express soil drought intensity and pasture drought intensity. The durations for different grades of drought events were correlated with both initial soil moisture and previous precipitation. The conclusions of this study can provide scientific references for the objective understanding onoccurrence, development, monitoring, and early warning of pasture drought.

 201506001 CCSF201611 CCSF201612 National Natural Science Foundation of China 41861013