Abstract
Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial. Here we use published data worldwide to examine the validity of Fuh's equation, which relates annual water yield (R) to a wetness index (precipitation/potential evapotranspiration; P/PET) and watershed characteristics (m). We identify two critical values at P/PET=1 and m=2. m plays a more important role than P/PET when m<2, and a lesser role when m>2. When P/PET<1, the relative water yield (R/P) is more responsive to changes in m than it is when P/PET>1, suggesting that any land cover changes in non-humid regions (P/PET<1) or in watersheds of low water retention capacity (m<2) can lead to greater hydrological responses. m significantly correlates with forest coverage, watershed slope and watershed area. This global pattern has far-reaching significance in studying and managing hydrological responses to land cover and climate changes.
Highlights
Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial
Where R/P is a dimensionless annual water yield coefficient; P/potential evapotranspiration (PET) is a dimensionless variable often called wetness index that differs by region and year, with its reciprocal (PET/P) often called dryness index; and m (1, N) is an integration constant that is dimensionless and independent of P and PET, and represents watershed characteristic[18,21]
We clarified the relative roles of climate and watershed characteristics on hydrological response
Summary
Research results on the effects of land cover change on water resources vary greatly and the topic remains controversial. M significantly correlates with forest coverage, watershed slope and watershed area This global pattern has far-reaching significance in studying and managing hydrological responses to land cover and climate changes. Especially in large watersheds, found that forest changes have limited effects[8], no effects[9,10] or even positive effects[11,12] on water yield These highly variable and apparently inconsistent results have led to debates in both research and resource management communities, especially when another catastrophic flood or drought occurs somewhere in the world[13]. A theoretical pattern on the dependence of the ratio of annual water yield to precipitation on wetness index (P/PET) and watershed characteristics (m) based on Fuh’s equation[18] is analysed and validated using the globally published data. The pattern explains the great variability in the effect of forest cover changes on water yield and implies that the effect can be negative, neutral or even positive, depending on the P/PET and m values of a watershed
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