Abstract: In this paper, an estimation model for water requirement of desert riparian forests was proposed. The model could achieve the target of daily calculation and reflect spatial variation of water requirement for different vegetation species by using normal meteorological data and vegetation parameters. Then, spatial and temporal distribution of water requirement of riparian forests in the lower reaches of Tarim River was analyzed using this model. The most important part of the model is α_p and K_b, which reflect the influence of different vegetation types and plant physiology respectively. The values of α_p·K_b in different growing periods in a vibrant growing Tamarix spp. stand and a Populus euphratica Oliv stand were acquired by fitting the data of measured ET and calculated ET₀ and fitting the data of ET/ET₀ and inversed leaf area index(LAI). Then, based on the meteorological data and remote sensing images of 2013 in the lower reaches of Tarim River, the spatio-temporal dynamics of riparian forests water requirement in the lower reaches of Tarim River was analyzed. Results showed as follows: (1)values of ET/ET₀ had a good correlation with the LAI in the germination and leaf expansion period and the leaf senescence period, and ET had a good correlation with ET₀ in the vibrant growing season, which indicated that the values of α p·K_b in the three different growing stages for tamarisk stand and P. euphratica stand were reasonable; (2)model checking based on observed data from the tamarisk stand indicated that this model could estimate water requirement and its daily dynamics of tamarisk stand with relatively high accuracy(NSE=0.780, RMSD= 0.677); (3)the annual total water requirement of the riparian forests was 1.035×10⁸m³, with the tamarisk forests 4.499×10⁷m³ and the P. euphratica forests 5.855×10⁷m³ in the existing vegetation distribution and coverage conditions. The average water requirement of the riparian forests per unite area was 139.6mm, the value of P. euphratica forests was 63mm more than tamarisk forests; (4)the whole riparian forests water requirement was relatively little in leaf expansion period(1.469×10⁷m³)and in leaf senescence period(0.641×10⁷m³), however, it was 8.244×10⁷m³ in vibrant growing season. The distribution of water requirement was connected with vegetation types and its coverage, the denser of the vegetation the more water it required. The model presented in this paper emphasized the impact of spatial variability of distribution of the desert riparian forests to water requirement, described time-space transformation and enhanced the estimation accuracy of water requirement and could provide more information and more accurate results for inland river resources management.

Key words: the lower reaches of Tarim River, desert riparian forests, Populus euphratica, tamarisk, vegetation water requirement