Statistical evaluation of remotely sensed snow-cover products with constraints from streamflow and SNOTEL measurements

Using streamflow and Snowpack Telemetry (SNOTEL) measurements as constraints, the evaluation of the Moderate Resolution Imaging Spectroradiometer (MODIS) daily and 8-day snow-cover products is carried out using the Upper Rio Grande River Basin as a test site. A time series of the snow areal extent (SAE) of the Upper Rio Grande Basin is retrieved from the MODIS tile h09v05 covering the time period from February 2000 to June 2004 using an automatic Geographic Information System (GIS)-based algorithm developed for this study. Statistical analysis between the streamflow at Otowi (NM) station and the SAE retrieved from the two MODIS snow-cover products shows that there is a statistically significant correlation between the streamflow and SAE for both products. This relationship can be disturbed by heavy rainstorms in the later springtime, especially in May. Correlation analyses show that the MODIS 8-day product has a better correlation (r=−0.404) with streamflow and has less percentage of spurious snowmelt events in wintertime than the MODIS daily product (r=−0.300). Intercomparison of these two products, with the SNOTEL data sets as the ground truth, shows that (1) the MODIS 8-day product has higher classification accuracy for both snow and land; (2) the omission error of misclassifying snow as land is similar for both products, both are low; (3) the MODIS 8-day product has a slightly higher commission error of misclassifying land as snow than the MODIS daily product; and (4) the MODIS daily product has higher omission errors of misclassifying both snow and land as clouds. Clouds are the major cause for reduction of the overall accuracy of the MODIS daily product. Improvement in suppressing clouds in the 8-day product is obvious from this comparison study. The sacrifice is the temporal resolution that is reduced from 1 to 8 days. The significance of the results is that the 8-day product will be more useful in evaluating the streamflow response to the snow-cover extent changes, especially from the long-term point of view considering its lower temporal resolution than the daily product. For clear days, the MODIS daily algorithm works quite well or even better than the MODIS 8-day algorithm.     

Stochastic Streamflow Simulation Using SAMS-2003

SAMS is a specialized software that has been developed for analyzing, modeling, and generating synthetic samples of hydrologic and water resources time series such as monthly streamflows. The 2003 version of SAMS provides enhanced technical capabilities from the earlier versions of the software. The graphical user interface and the mechanisms for handling the data have been entirely rewritten in MS Visual C++. As a result SAMS-2003 is easier to use and easier to update and maintain. In addition, substantial changes and restructuring have been made to enhance the modeling and data generation capabilities. The package provides many menu option windows that focus on three primary application modules—statistical analysis of data, fitting of a stochastic model (including parameter estimation and testing), and generating synthetic series. SAMS has the capability of analyzing and modeling single site and multisite annual and seasonal data such as monthly and weekly streamflows based on a number of single site and multisite stochastic models, and aggregation and disaggregation modeling schemes. The models are then utilized for generating synthetic data. Results from the various computations, e.g., the generated samples, can be presented in graphical and tabular forms and, if desired, saved to an output file. Some illustrations are provided to demonstrate the improved technical capabilities of the program using flow data of the Colorado River system.     

Flow Depletion Induced by Pumping Well from Stream Perpendicularly Intersecting Impermeable/Recharge Boundary

Analytical solutions for rate and volume of flow depletion induced by pumping a well from a stream that intersects an impermeable or a recharge boundary at right angles are derived using the basic flow depletion factor defined earlier by the author. A new concept of directly obtaining stream flow depletion using the method of images is proposed. The solutions are derived for five different management cases of a stream and boundary intersecting at right-angles, assuming the aquifer to be confined with semi-infinite areal extent. A computationally simple function is proposed for accurately approximating the error function. The existing analytical solution in the case of a right-angle bend of stream given by Hantush was obtained for unconfined aquifers using a linearization of the governing partial differential equation. The solution for this case obtained using the proposed method for confined aquifer is the same as obtained by Hantush for unconfined aquifers, which shows that the linearization adopted by Hantush does not actually solve this problem for unconfined aquifers.