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Juan B. Valdés

Bio: Juan B. Valdés is an academic researcher from University of Arizona. The author has contributed to research in topics: Precipitation & Water resources. The author has an hindex of 35, co-authored 136 publications receiving 5092 citations. Previous affiliations of Juan B. Valdés include NASA Headquarters & United States Army Corps of Engineers.


Papers
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Journal ArticleDOI
TL;DR: In this article, a unified synthesis of the hydrologic response of a catchment to surface runoff is attempted by linking the instantaneous unit hydrograph (IUH) with the geomorphologic parameters of a basin.
Abstract: A unifying synthesis of the hydrologic response of a catchment to surface runoff is attempted by linking the instantaneous unit hydrograph (IUH) with the geomorphologic parameters of a basin. Equations of general character are derived which express the IUH as a function of Horton's numbers RA, RB, and RL; an internal scale parameter LΩ and a mean velocity of streamflow v. The IUH is time varying in character both throughout the storm and for different storms. This variability is accounted for by the variability in the mean streamflow velocity. The underlying unity in the nature of the geomorphologic structure is thus carried over to the great variety of hydrologic responses that occur in nature. An approach is initiated to the problem of hydrologic similarity.

1,007 citations

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TL;DR: Droughts are destructive climatic extreme events that may cause significant damage both in natural environments and in human lives.
Abstract: Droughts are destructive climatic extreme events that may cause significant damage both in natural environments and in human lives. Drought forecasting plays an important role in the control and ma...

416 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the current predictive capability of general circulation models linked with macro-scale and landscape-scale hydrologic models that simulate regional and local hydrological regimes under global warming scenarios.

275 citations

Journal ArticleDOI
TL;DR: In this article, climate change scenarios were created from scaling factors derived from several general circulation models to assess the likely impacts of aquifer pumping on the water resources of the Edwards Balcones Fault Zone (BFZ) aquifer, Texas, one of the largest aquifer systems in the United States.

215 citations

Journal ArticleDOI
TL;DR: In this paper, an assessment of the importance of precipitation accuracy on the rainfall-runoff modeling of a small catchment was performed using two mathematical models: a deterministic rainfall runoff model based on the kinematic wave approximation and a nonstationary time-varying multidimensional rainfall generation model.
Abstract: This study is an assessment of the importance of precipitation accuracy on the rainfall-runoff modeling of a small catchment Two mathematical models were used in the investigation: a deterministic rainfall-runoff model based on the kinematic wave approximation and a nonstationary time-varying multidimensional rainfall generation model It is implicitly assumed that this rainfall generation model is an appropriate mathematical representation of the natural phenomenon of rainfall The deterministic rainfall-runoff model is used to represent the 265-mi2 catchment of the Rio Fajardo in northeastern Puerto Rico The rainfall model generates synthetic rainfall which serves as the input to this runoff model The influence of the spatial distribution of the rainfall input on the discharge is analyzed by using 1 rain gage or 20 rain gages to record the synthetic storms The isohyetal maps and hyetographs of the synthetic storms, together with the storm hydrographs produced by the runoff model, are analyzed, with specific attention given to the volume of storm runoff, time-to-peak runoff, and peak runoff The experiments show that the spatial distribution of rain and the accuracy of the precipitation input have a marked influence on the outflow hydrograph from a small catchment

186 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a new climatic drought index, the standardized precipitation evapotranspiration index (SPEI), is proposed, which combines multiscalar character with the capacity to include the effects of temperature variability on drought assessment.
Abstract: The authors propose a new climatic drought index: the standardized precipitation evapotranspiration index (SPEI). The SPEI is based on precipitation and temperature data, and it has the advantage of combining multiscalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a log-logistic probability distribution. Mathematically, the SPEI is similar to the standardized precipitation index (SPI), but it includes the role of temperature. Because the SPEI is based on a water balance, it can be compared to the self-calibrated Palmer drought severity index (sc-PDSI). Time series of the three indices were compared for a set of observatories with different climate characteristics, located in different parts of the world. Under global warming conditions, only the sc-PDSI and SPEI identified an...

5,088 citations

Journal Article
TL;DR: In this article, the authors present a document, redatto, voted and pubblicato by the Ipcc -Comitato intergovernativo sui cambiamenti climatici - illustra la sintesi delle ricerche svolte su questo tema rilevante.
Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

4,187 citations

Journal ArticleDOI
TL;DR: In this paper, the authors provide a review of fundamental concepts of drought, classification of droughts, drought indices, historical Droughts using paleoclimatic studies, and the relation between DAs and large scale climate indices.

3,352 citations

01 Apr 2003
TL;DR: The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it as mentioned in this paper, and also presents new ideas and alternative interpretations which further explain the success of the EnkF.
Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

2,975 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications.
Abstract: The topography of a catchment has a major impact on the hydrological, geomorphological. and biological processes active in the landscape. The spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques. Many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems. Furthermore, topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology. Digital elevation models are the primary data used in the analysis of catchment topography. We describe elevation data sources, digital elevation model structures, and the analysis of digital elevation data for hydrological, geomorphological, and biological applications. Some hydrologic models that make use of digital representations of topography are also considered.

2,855 citations