Search Results

You are looking at 1 - 2 of 2 items for :

  • Author or Editor: Konrad Steffen x
  • Journal of Hydrometeorology x
  • Refine by Access: All Content x
Clear All Modify Search
Sebastian H. Mernild
,
Glen E. Liston
,
Christopher A. Hiemstra
, and
Konrad Steffen

Abstract

SnowModel, a physically based snow-evolution modeling system that includes four submodels—MicroMet, EnBal, SnowPack, and SnowTran-3D—was used to simulate variations in Greenland [including the Greenland Ice Sheet (GrIS)] surface snow and ice melt, as well as water balance components, for 1995–2005. Meteorological observations from 25 stations inside and outside the GrIS were used as model input. Winter and summer mass balance observations, spatial snow depth observations, and snowmelt depletion curves derived from time-lapse photography from the Mittivakkat and Zackenberg glacierized catchments in East Greenland were used to validate the performance of SnowModel. Model results compared well with observed values, confirming the robustness of the model. The yearly modeled GrIS interior nonmelt area differs from satellite observations by a maximum of ∼68 000 km2 (or ∼6%) in 2004, and the lowest uncertainties (<8000 km2, or <1%) occur for the years with the smallest (2005) and most extensive (1996) nonmelt areas. Modeled surface melt occurred at elevations reaching 2950 m MSL for 2005, while the equilibrium line altitude (ELA) fluctuates from 1640 to 600 m MSL. The modeled interannual variability in the nonmelt area also agrees with observation records (R 2 = 0.96), yielding simulated GrIS nonmelt covers of 71% for 1996 and 50% for 2005. On average, the simulated nonmelt area decreased ∼6% from 1995 to 2005; this trend is similar to observed values. An average surface mass balance (SMB) storage of 138(±81) km3 yr−1, a GrIS loss of 257(±81) km3 yr−1, and a runoff contribution to the ocean of 392(±58) km3 yr−1 occurred for the period 1995–2005. Approximately 58% and 42% of the runoff came from the GrIS western and eastern drainage areas, respectively. The modeled average specific runoff from the GrIS was 6.71 s−1 km−2 yr−1, which, over the simulation period, represents a contribution of ∼1.1 mm yr−1 to global sea level rise.

Full access
Joseph G. Alfieri
,
Peter D. Blanken
,
David N. Yates
, and
Konrad Steffen

Abstract

Nearly one-half of the earth’s terrestrial surface is susceptible to drought, which can have significant social, economic, and environmental impacts. Therefore, it is important to develop better descriptions and models of the processes linking the land surface and atmosphere during drought. Using data collected during the International H2O Project, the study presented here investigates the effects of variations in the environmental factors driving the latent heat flux (λE) during drought conditions at a rangeland site located in the panhandle of Oklahoma. Specifically, this study focuses on the relationships of λE with vapor pressure deficit, wind speed, net radiation, soil moisture content, and greenness fraction. While each of these environmental factors has an influence, soil moisture content is the key control on λE. The role of soil moisture in regulating λE is explained in terms of the surface resistance to water vapor transfer. The results show that λE transitioned between being water or energy limited during the course of the drought. The implications of this on the ability to understand and model drought conditions and transitions into or out of droughts are discussed.

Full access