Evaluation of Satellite-Derived Products for the Daily Average and Extreme Rainfall in the Mearim River Drainage Basin (Maranhão, Brazil)

Satellite precipitation estimates are used as an alternative or as a supplement to the records of the in situ stations. Although some satellite precipitation products have reasonably consistent time series, they are often limited to specific geographic areas. The main objective of this study was to evaluate CHIRPS version 2, MSWEP version 2, and PERSIANN-CDR, compared to gridBR, as daily mean and extreme inputs represented on a monthly scale and their respective seasonal trends of rainfall in the Mearim River Drainage Basin (MDB), Maranhão state, Brazil. Estimates of errors were calculated (relative error, pbias; root mean square error, RMSE, and Willmott concordance index, d), and the chances of precipitation were estimated by remote sensing (RES). In addition, trends in precipitation were estimated by the two-sample Mann–Kendall test. Given the overall performance, the best products for estimating monthly mean daily rainfall in the MDB are CHIRPS and PERSIANN-CDR, especially for rainy months (December to May). For daily extremes on the monthly scale, the best RES is PERSIANN-CDR. There is no general agreement between gridBR and RES methods for the trend signal, even a nonsignificant one, much less a significant one. The use of MSWEP for the MDB region is discouraged by this study because it overestimates monthly averages and extremes. Finally, studies of this kind in drainage basins are essential to improve the information generated for managing territories and developing regionalized climate and hydrological models.

G.K. Gilbert and the Bonneville shoreline

The Bonneville shoreline, the highest, and second-most prominent shoreline of Pleistocene Lake Bonneville in Utah, Nevada, and Idaho, has been thought for many years to have formed during a period ofprolonged overflow (500 to 1000+ years) and lake-level stability prior to the Bonneville flood. That traditional idea was initially promoted by G.K. Gilbert during the 1870s before he spent over a decade on field work related to Lake Bonneville. During Gilbert’s field work, his observations led him to a different interpretation of how the Bonneville shoreline developed, and by the time his final report on Lake Bonneville was published in 1890, he was no longer promoting the idea of prolonged overflow. Instead he thought of the Bonneville shoreline as a geomorphic record of the highest level attained by the transgressing lake in the closed basin; the shoreline marks the boundary between lacustrine-dominated landforms below and fluvial-dominated landforms above. For over 120 years after Gilbert’s (1890) monograph was published, researchers ignored his interpretation, and assumed (but did not present supporting evidence), that Lake Bonneville had overflowed for a prolonged period prior to the Bonneville flood while the Bonneville shoreline developed. Re-examination of the geomorphology of the Bonneville shoreline, the stratigraphy of Lake Bonneville deposits, the geomorphology of the overflow area, and the history of Lake Bonneville, shows that Gilbert’s 1890 interpretation is consistent with observations. Considering this, to accurately interpret the history of Lake Bonneville the Bonneville shoreline should be viewed as the level the lake had reached in the closed basin when its transgression ceased and it began to spill into the Snake River drainage basin.

Does Antarctic Oscillation have links and influence precipitation over the Uruguay River Drainage Basin in Southeastern South America?

This article examines the links and the influence of Antarctic Oscillation (AAO) on precipitation over the Uruguay River Drainage Basin and adjacent regions, situated in Southeastern South America. In this article, we used monthly data of AAO Index obtained from the Climate Prediction Center/National Centers for Environmental Prediction (CPC/NCEP); monthly data of 500 hPa vertical motion through omega variable (ω = Dp/Dt) and converted to vertical velocity (cm/s) from the NCEP/NCAR Reanalysis; monthly data of precipitation from the NCEP Reanalysis 2 and monthly data of precipitation rate from the CPC Merged Analysis of Precipitation (CMAP) with a latitude × longitude spatial resolution of 2.5° × 2.5°. All data are monthly means and were obtained from January 1979 to December 2008. The methodological procedures used Grid Analysis and Display System (GrADS) software to generate composites of vertical motion and precipitation rates. In the case of CMAP precipitation data, the methodology consists of applying the Aspin Welch statistical test, which verifies the statistical significance of the difference between two means using a significance level of 5%. The study region indicates a tendency to present higher (lower) mean rates of precipitation during the AAO negative (positive) phase. The vertical motion analysis results corroborate with the precipitation rates since the higher vertical motions were found during the negative phase of AAO. The statistical test showed, to some areas of Uruguay River Drainage Basin and adjacent regions, statistically significant differences between mean rates of precipitation observed in both phases of AAO.