HR: 08:45h
AN: GC51B-04    [Abstracts]
TI: Variability of basin-scale terrestrial water storage from a novel application of the water budget equation: the Amazon and the Mississippi
AU: Yoon, J
EM: yjinho@atmos.umd.edu
AF: University of Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AU: * Zeng, N
EM: zeng@atmos.umd.edu
AF: University of Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AU: Mariotti, A
EM: amariott@essic.umd.edu
AF: University of Maryland, AOSC and ESSIC, College Park, MD 20742, United States
AU: Swenson, S
EM: swensosc@colorado.edu
AF: U Colorado, CIRES, Boulder, CO 80309, United States
AB: In an approach termed the P-E-R (or simply PER) method, we apply the basin water budget equation to diagnose the long-term variability of the total terrestrial water storage (TWS). The key input variables are observed precipitation (P) and runoff (R), and estimated evaporation (E). Unlike typical offline land-surface model estimate where only atmospheric variables are used as input, the direct use of observed runoff in the PER method imposes an important constraint on the diagnosed TWS. Although there lack basin-scale observations of evaporation, the tendency of E to have significantly less variability than the difference between precipitation and runoff (P-R) minimizes the uncertainties originating from estimated evaporation. Compared to the more traditional method using atmospheric moisture convergence (MC) minus R (MCR method), the use of observed precipitation in PER method is expected to lead to general improvement, especially in regions atmospheric radiosonde data are too sparse to constrain the atmospheric model analyzed MC such as in the remote tropics. TWS was diagnosed using the PER method for the Amazon (1970-2006) and the Mississippi Basin (1928-2006), and compared with MCR method, land-surface model and reanalyses, and NASA's GRACE satellite gravity data. The seasonal cycle of diagnosed TWS over the Amazon is about 300 mm. The interannual TWS variability in these two basins are 100-200 mm, but multi-dacadal changes can be as large as 600-800 mm. Major droughts such as the Dust Bowl period had large impact with water storage depleted by 500 mm over a decade. Within the short period 2003-2006 when GRACE data was available, PER and GRACE show good agreement both for seasonal cycle and interannual variability, providing potential to cross-validate each other. In contrast, land-surface model results are significantly smaller than PER and GRACE, especially towards longer timescales. While we currently lack independent means to verify these long-term changes, simple error analysis using 3 precipitation datasets and 3 evaporation estimates suggest that the multi-decadal amplitude can be uncertain up to a factor of 2, while the agreement is high on interannual timescales. The large TWS variability implies the remarkable capacity of land-surface in storing and taking up water that may be under-represented in models. The results also suggest the existence of water storage memories on multi-year time scales, significantly longer than typically assumed seasonal timescales associated with surface soil moisture.
DE: 1218 Mass balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532)
DE: 1807 Climate impacts
DE: 1812 Drought
DE: 1829 Groundwater hydrology
DE: 1876 Water budgets
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting