Comment on 'Shang S. 2012. Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step. Hydrological Processes 26: 3338-3343. DOI: 10.1002/hyp.8405'

A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ET(sub a)) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ET(sub a) over limited soil-water ranges in a root zone drying out due to evapotranspiration. It then used a single crop-soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ET(sub c)). This comment reformulates those ET(sub a) equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ET(sub a) on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop-soil composite can be invalid for other crop-soil composites. Finally, a consideration of the numerical error in the time-cumulative value of ET(sub a) is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ET(sub a) is more relevant to the final crop yield

Drought Prediction for Socio-Cultural Stability Project

The primary objective of this project is to answer the question: "Can existing, linked infrastructures be used to predict the onset of drought months in advance?" Based on our work, the answer to this question is "yes" with the qualifiers that skill depends on both lead-time and location, and especially with the associated teleconnections (e.g., ENSO, Indian Ocean Dipole) active in a given region season. As part of this work, we successfully developed a prototype drought early warning system based on existing/mature NASA Earth science components including the Goddard Earth Observing System Data Assimilation System Version 5 (GEOS-5) forecasting model, the Land Information System (LIS) land data assimilation software framework, the Catchment Land Surface Model (CLSM), remotely sensed terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE) and remotely sensed soil moisture products from the Aqua/Advanced Microwave Scanning Radiometer - EOS (AMSR-E). We focused on a single drought year - 2011 - during which major agricultural droughts occurred with devastating impacts in the Texas-Mexico region of North America (TEXMEX) and the Horn of Africa (HOA). Our results demonstrate that GEOS-5 precipitation forecasts show skill globally at 1-month lead, and can show up to 3 months skill regionally in the TEXMEX and HOA areas. Our results also demonstrate that the CLSM soil moisture percentiles are a goof indicator of drought, as compared to the North American Drought Monitor of TEXMEX and a combination of Famine Early Warning Systems Network (FEWS NET) data and Moderate Resolution Imaging Spectrometer (MODIS)'s Normalizing Difference Vegetation Index (NDVI) anomalies over HOA. The data assimilation experiments produced mixed results. GRACE terrestrial water storage (TWS) assimilation was found to significantly improve soil moisture and evapotransportation, as well as drought monitoring via soil moisture percentiles, while AMSR-E soil moisture assimilation produced marginal benefits. We carried out 1-3 month lead-time forecast experiments using GEOS-5 forecasts as input to LIS/CLSM. Based on these forecast experiments, we find that the expected skill in GEOS-5 forecasts from 1-3 months is present in the soil moisture percentiles used to indicate drought. In the case of the HOA drought, the failure of the long rains in April appears in the February 1, March 1 and April 1 initialized forecasts, suggesting that for this case, drought forecasting would have provided some advance warning about the drought conditions observed in 2011. Three key recommendations for follow-up work include: (1) carry out a comprehensive analysis of droughts observed over the entire period of record for GEOS-5 forecasts; (2) continue to analyze the GEOS-5 forecasts in HOA stratifying by anomalies in long and short rains; and (3) continue to include GRACE TWS, Soil Moisture/Ocean Salinity (SMOS) and the upcoming NASA Soil Moisture Active/Passive (SMAP) soil moisture products in a routine activity building on this prototype to further quantify the benefits for drought assessment and prediction

Evaluation of the hydro-thermodynamic soil-vegetation scheme on the basis of observations and a Galerkin type finite element numerical scheme

Thesis (M.S.) University of Alaska Fairbanks, 2005The Hydro-Thermodynamic Soil- vegetation Scheme (HTSYS), coupled in a two-way mode with the PennState/National Center for Atmospheric Research (NCAR) Mesoscale Meteorological Model generation 5 (MM5), has been evaluated for a 5 day typical snow-melt period using the Baltic Sea experiment meteorological data center's soil temperature, snow depth, and precipitation datasets. The HTSVS-MM5 evaluation investigates the coupled system's sensitivity to two cloud models and two radiation models, with their cross effects presented along with skill scores for snow depth changes. The coupled model satisfactorily predicts the soil temperature diurnal course cycles, changes in the snow depths, and accumulated precipitation. HTSVS's soil model has been further tested and evaluated in an offline mode for the advanced numerical treatment for the Partial Differential Equations (PDEs) using soil temperature datasets from three sites at Council, Alaska. A Galerkin Weak Finite Element (GWFE) method was tested and evaluated for the numerical treatment of PDEs and the predictions were compared against the existing Crank-Nicholson finite differences scheme (CNFD). GWFE solutions exhibit a remarkable soil temperature predictability, better capture the temperature peaks, and yield non-diffuse and non-oscillatory solutions for relatively high convection dominated regimes, while CNFD performs comparably well in diffusion dominated regimes with a lower computational burden

Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step.

A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ETa) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ETa over limited soil-water ranges in a root zone drying out due to evapotranspiration. It then used a single crop-soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ETc). This comment reformulates those ETa equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ETa on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop-soil composite can be invalid for other crop-soil composites. Finally, a consideration of the numerical error in the time-cumulative value of ETa is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ETa is more relevant to the final crop yield. Published 2014. This article is a U.S. Government work and is in the public domain in the USA

Covariations between the Indian Oceandipole and ENSO: a modeling study

The coevolution of the Indian Ocean dipole (IOD) and El Niño-Southern Oscillation (ENSO) is examined using both observational data and coupled global climate model simulations. The covariability of IOD and ENSO is analyzed by applying the extended empirical orthogonal function (EEOF) method to the surface and subsurface ocean temperatures in the tropical Indian Ocean and western Pacifc. The frst EEOF mode shows the evolution of IOD that lags ENSO, whereas the second mode exhibits the transition from a dipole mode to a basin-wide mode in the tropical Indian Ocean that leads ENSO. The lead-lag relationships between IOD and ENSO are consistent with two-way interactions between them. A comparison between two 500-year model simulations with and without ENSO shows that ENSO can enhance the variability of IOD at interannual time scale. The infuence of ENSO on the IOD intensity is larger for the eastern pole than for the western pole, and further, is stronger in the negative IOD phase than in the positive phase. The infuence of IOD on ENSO is demonstrated by the improvement of ENSO prediction using sea surface temperature (SST) in the tropical Indian Ocean as an ENSO precursor. The improvement of the ENSO forecast skill is found at both a short lead time (0 month) and long leads (10–15 months). The SST in the western pole has more predictive value than in the eastern pole. The eastward propagation of surface and subsurface temperature signals from the western Indian Ocean that precedes the development of heat content anomaly in the tropical western Pacifc is the key for extending the lead time for ENSO prediction. Our results are consistent with previously reported fndings but highlight the spatial–temporal evolution of the ENSO-IOD system. It is also illustrated that IOD would have been more helpful in predicting the 1997/98 El Niño than the 2015/16 El Niño

The role of atmospheric internal variability on the tropical instability wave dynamics

The impact of atmospheric internal variability on tropical instability wave (TIW) activity in the eastern equatorial Pacific is examined. To diagnose the atmospheric internal variability, two simulations were performed with a state‐of‐the‐art coupled general circulation model that uses an eddy permitting ocean component model. Standard coupling procedures are implemented in the control simulation. In the experimental simulation, the so‐called interactive ensemble coupling is used, which systematically reduces the contribution of internal atmospheric dynamics to the air‐sea fluxes of heat, momentum and fresh water. In the eastern equatorial Pacific, the reduction of the atmospheric internal variability leads to an enhancement of the available potential energy and higher exchanges from mean to eddy potential energy. The perturbations in the available potential energy and the eddy potential energy contribute to the enhancement in the TIW activity through the increased eddy kinetic energy. Due to the negative correlation between the atmospheric internal variability and TIW activity, the covariance between the momentum flux at the air‐sea interface and the ocean surface currents as well as heat flux at the air‐sea interface and the sea surface temperatures were nearly conserved west of 120°W between the control and the experimental simulations.Key PointsThe role of weather noise on tropical instability wave dynamicsAir‐sea interaction in the tropical PacificAtmospheric internal variability on ocean internal variabilit

Bias correction methods for decadal sea-surface temperature forecasts

Two traditional bias correction techniques: (1) systematic mean correction (SMC) and (2) systematic least-squares correction (SLC) are extended and applied on sea-surface temperature (SST) decadal forecasts in the North Pacific produced by Climate Forecast System version 2 (CFSv2) to reduce large systematic biases. The bias-corrected forecast anomalies exhibit reduced root-mean-square errors and also significantly improve the anomaly correlations with observations. The spatial pattern of the SST anomalies associated with the Pacific area average (PAA) index (spatial average of SST anomalies over 20°–60°N and 120°E–100°W) is improved after employing the bias correction methods, particularly SMC. Reliability diagrams show that the bias-corrected forecasts better reproduce the cold and warm events well beyond the 5-yr lead-times over the 10 forecasted years. The comparison between both correction methods indicates that: (1) prediction skill of SST anomalies associated with the PAA index is improved by SMC with respect to SLC and (2) SMC-derived forecasts have a slightly higher reliability than those corrected by SLC