Waldo Lavado

A Comparative Performance Analysis of TRMM 3B42 (TMPA) Versions 6 and 7 for Hydrological Applications over Andean–Amazon River Basins

AbstractThe Tropical Rainfall Measuring Mission 3B42 precipitation estimates are widely used in tropical regions for hydrometeorological research. Recently, version 7 of the product was released. Major revisions to the algorithm involve the radar reflectivity–rainfall rate relationship, surface clutter detection over high terrain, a new reference database for the passive microwave algorithm, and a higher-quality gauge analysis product for monthly bias correction. To assess the impacts of the improved algorithm, the authors compare the version 7 and the older version 6 products with data from 263 rain gauges in and around the northern Peruvian Andes. The region covers humid tropical rain forest, tropical mountains, and arid-to-humid coastal plains. The authors find that the version 7 product has a significantly lower bias and an improved representation of the rainfall distribution. They further evaluated the performance of the version 6 and 7 products as forcing data for hydrological modeling by comparing ...

Climate variability and extreme drought in the upper Solimões River (western Amazon Basin): Understanding the exceptional 2010 drought

This work provides an initial overview of climate features and their related hydrological impacts during the recent extreme droughts (1995, 1998, 2005 and 2010) in the upper Solimoes River (western Amazon), using comprehensive in situ discharge and rainfall datasets. The droughts are generally associated with positive SST anomalies in the tropical North Atlantic and weak trade winds and water vapor transport toward the upper Solimoes, which, in association with increased subsidence over central and southern Amazon, explain the lack of rainfall and very low discharge values. But in 1998, toward the end of the 1997-98 El Nino event, the drought is more likely related to an anomalous divergence of water vapor in the western Amazon that is characteristic of a warm event in the Pacific. During the austral spring and winter of 2010, the most severe drought since the seventies has been registered in the upper Solimoes. Its intensity and its length, when compared to the 2005 drought, can be explained by the addition of an El Nino in austral summer and a very warm episode in the Atlantic in boreal spring and summer. As in 2005, the lack of water in 2010 was more important in the southern tropical tributaries of the upper Solimoes than in the northern ones.

The Major Floods in the Amazonas River and Tributaries (Western Amazon Basin) during the 1970–2012 Period: A Focus on the 2012 Flood*

In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River during the 1970‐2012 period, focusing on the recent April 2012 flooding (55400m 3 s 21 ). Several hydrological variables, such as rainfall, terrestrial water storage, and discharge, point out that the unprecedented 2012 flood is mainlyrelatedtoanearlyandabundantwetseasonoverthenorthofthebasin.Thus,thepeakoftheMara~� River, the northern contributor of the Amazonas, occurred sooner than usual (in April instead of May), coinciding with the peak of the Ucayali River, the southerncontributor.This concomitance caused a dramatic flood downstream in the Peruvian Amazonas. These results are compared to the amplitude and timing of the three most severe extreme floods (1970‐2011). The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 2012) suggests that they are characterized by a La Ni~ event, which originates a geopotential height wave train near the ground, with positive anomalies over the subtropical South and North Pacific and Atlantic and over southeastern South America. These patterns contribute to 1) the origin of an abundant humidity transport flux from the tropical North Atlantic and the Caribbean Sea toward the northwestern Amazon and 2) the maintenance of the monsoon flux over this region. They both favor a strong convergence of humidity in the northern Amazonas basin. Finally, the authors suggest that the intensity of floods is more likely related to an early La Ni~ event (as observed during the 2011/12 season), early rainfall, and simultaneous peaks of both tributaries of the Amazonas River.

Rainfall hotspots over the southern tropical Andes: Spatial distribution, rainfall intensity, and relations with large-scale atmospheric circulation

The Andes/Amazon transition is among the rainiest regions of the world and the interactions between large-scale circulation and the topography that determine its complex rainfall distribution remain poorly known. This work provides an in-depth analysis of the spatial distribution, variability, and intensity of rainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis is based on comprehensive daily rainfall data sets from meteorological stations in Peru and Bolivia. We compare our results with high-resolution rainfall TRMM-PR 2A25 estimations. Hotspot regions are identified at low elevations in the Andean foothills (400–700 masl) and in windward conditions at Quincemil and Chipiriri, where more than 4000 mm rainfall per year are recorded. Orographic effects and exposure to easterly winds produce a strong annual rainfall gradient between the lowlands and the Andes that can reach 190 mm/km. Although TRMM-PR reproduces the spatial distribution satisfactorily, it underestimates rainfall by 35% in the hotspot regions. In the Peruvian hotspot, exceptional rainfall occurs during the austral dry season (around 1000 mm in June–July–August; JJA), but not in the Bolivian hotspot. The direction of the low-level winds over the Andean foothills partly explains this difference in the seasonal rainfall cycle. At intraseasonal scales in JJA, we found that, during northerly wind regimes, positive rainfall anomalies predominate over the lowland and the eastern flank of the Andes, whereas less rain falls at higher altitudes. On the other hand, during southerly regimes, rainfall anomalies are negative in the hotspot regions. The influence of cross-equatorial winds is particularly clear below 2000 masl.

From drought to flooding: understanding the abrupt 2010-11 hydrological annual cycle in the Amazonas River and tributaries

In this work we document and analyze the hydrological annual cycles characterized by a rapid transition between low and high flows in the Amazonas River (Peruvian Amazon) and we show how these events, which may impact vulnerable riverside residents, are related to regional climate variability. Our analysis is based on comprehensive discharge, rainfall and average suspended sediment data sets. Particular attention is paid to the 2010‐11 hydrological year, when an unprecedented abrupt transition from the extreme September 2010 drought (8300 m 3 s 1 / to one of the four highest discharges in April 2011 (49 500 m 3 s 1 / was recorded at Tamshiyacu (Amazonas River). This unusual transition is also observed in average suspended sediments. Years with a rapid increase in discharge are characterized by negative sea surface temperature anomalies in the central equatorial Pacific during austral summer, corresponding to a La Ni˜ na-like mode. It originates a geopotential height wave train over the subtropical South Pacific and southeastern South America, with a negative anomaly along the southern Amazon and the southeastern South Atlantic convergence zone region. As a consequence, the monsoon flux is retained over the Amazon and a strong convergence of humidity occurs in the Peruvian Amazon basin, favoring high rainfall and discharge. These features are also reported during the 2010‐11 austral summer, when an intense La Ni˜ na event characterized the equatorial Pacific.

High‐resolution satellite‐gauge merged precipitation climatologies of the Tropical Andes

Satellite precipitation products are becoming increasingly useful to complement rain gauge networks in regions where these are too sparse to capture spatial precipitation patterns, such as in the Tropical Andes. The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (TPR) was active for 17 years (1998–2014) and has generated one of the longest single-sensor, high-resolution, and high-accuracy rainfall records. In this study, high-resolution (5 km) gridded mean monthly climatological precipitation is derived from the raw orbital TPR data (TRMM 2A25) and merged with 723 rain gauges using multiple satellite-gauge (S-G) merging approaches. The resulting precipitation products are evaluated by cross validation and catchment water balances (runoff ratios) for 50 catchments across the Tropical Andes. Results show that the TPR captures major synoptic and seasonal precipitation patterns and also accurately defines orographic gradients but underestimates absolute monthly rainfall rates. The S-G merged products presented in this study constitute an improved source of climatological rainfall data, outperforming the gridded TPR product as well as a rain gauge-only product based on ordinary Kriging. Among the S-G merging methods, performance of inverse distance interpolation of satellite-gauge residuals was similar to that of geostatistical methods, which were more sensitive to gauge network density. High uncertainty and low performance of the merged precipitation products predominantly affected regions with low and intermittent precipitation regimes (e.g., Peruvian Pacific coast) and is likely linked to the low TPR sampling frequency. All S-G merged products presented in this study are available in the public domain.