Relating seasonal dynamics of enhanced vegetation index to the recycling of water in two endorheic river basins in north-west China
This study associates the dynamics of enhanced vegetation index in lowland desert oases to the recycling of water in two endorheic (hydrologically closed) river basins in Gansu Province, north-west China, along a gradient of elevation zones and land cover types. Each river basin was subdivided into...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-08-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/19/3387/2015/hess-19-3387-2015.pdf |
| Summary: | This study associates the dynamics of enhanced vegetation index in lowland
desert oases to the recycling of water in two endorheic (hydrologically
closed) river basins in Gansu Province, north-west China, along a gradient of
elevation zones and land cover types. Each river basin was subdivided into
four elevation zones representative of (i) oasis plains and foothills, and
(ii) low-, (iii) mid-, and (iv) high-mountain elevations. Comparison of
monthly vegetation phenology with precipitation and snowmelt dynamics within
the same basins over a 10-year period (2000–2009) suggested that the onset
of the precipitation season (cumulative % precipitation > 7–8 %)
in the mountains, typically in late April to early May, was triggered by the
greening of vegetation and increased production of water vapour at the base
of the mountains. Seasonal evolution of in-mountain precipitation correlated
fairly well with the temporal variation in oasis-vegetation coverage and
phenology characterised by monthly enhanced vegetation index, yielding
coefficients of determination of 0.65 and 0.85 for the two basins. Convergent
cross-mapping of related time series indicated bi-directional causality
(feedback) between the two variables. Comparisons between same-zone monthly
precipitation amounts and enhanced vegetation index provided weaker
correlations. Start of the growing season in the oases was shown to coincide
with favourable spring warming and discharge of meltwater from low- to
mid-elevations of the Qilian Mountains (zones 1 and 2) in mid-to-late March.
In terms of plant requirement for water,
mid-seasonal development of oasis vegetation was seen to be controlled to a
greater extent by the production of rain in the mountains. Comparison of
water volumes associated with in-basin production of rainfall and snowmelt
with that associated with evaporation seemed to suggest that about 90 %
of the available liquid water (i.e. mostly in the form of direct rainfall and
snowmelt in the mountains) was recycled locally. |
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| ISSN: | 1027-5606 1607-7938 |