Evapotranspiration along an elevation gradient 2 in California ’ s Sierra Nevada

6 [1] We combined observations from four eddy covariance towers with remote sensing to 7 better understand the altitudinal patterns of climate, plant phenology, Gross Ecosystem 8 CO2 Uptake, and Evapotranspiration (ET) around the upper Kings River basin in the 9 southern Sierra Nevada Mountains. Precipitation (P) increased with elevation to 500 m, 10 and more gradually at higher elevations, while vegetation graded from savanna at 405 m to 11 evergreen oak and pine forest to mid-montane forest to subalpine forest at 2700 m. 12 CO2 uptake and transpiration at 405 m peaked in spring (March to May) and declined in 13 summer; gas exchange at 1160 and 2015 m continued year-round; gas exchange at 2700 m 14 peaked in summer and ceased in winter. A phenological threshold occurred between 2015 15 and 2700 m, associated with the development of winter dormancy. Annual ET and Gross 16 Primary Production were greatest at 1160 and 2015 m and reduced at 405 m coincident 17 with less P, and at 2700 m coincident with colder temperatures. The large decline in ET 18 above 2015 m raises the possibility that an upslope redistribution of vegetation with 19 climate change could cause a large increase in upper elevation ET. We extrapolated ET to 20 the entire basin using remote sensing. The 2003–11 P for the entire upper Kings River 21 basin was 984 mmy 1 and the ET was 429 mmy , yielding a P-ET of 554 mmy , which 22 agrees well with the observed Kings River flow of 563 mmy . ET averaged across the 23 entire basin was nearly constant from year to year.