Runoff from agricultural fields is a significant non-point source of pollution to water bodies, as it transports sediments, nutrients, pesticides, and veterinary pharmaceuticals (VA). Climate change intensifies the hydrological cycle, generating more extreme hydrometeorological and climate conditions (EHCC) that lead to floods and droughts. However, there is limited information regarding those impacts on water quality in agricultural areas. The aim of this dissertation is to evaluate the occurrence of VA and streamflow response to EHCC in the Shell Creek (SC) watershed, Nebraska. Streamflow and water quality are simulated using the Soil and Water Assessment Tool (SWAT). VA are detected using Polar Organic Chemical Integrative Samplers (POCIS) and simulated using the pesticide subroutine in SWAT. Model performance is measured by the Nash-Sutcliffe Efficiency (NSE) coefficient. Streamflow ...

The frequency of rainfall is relevant for agriculture because its distribution affects crop production. Few stochastic models successfully generate daily rainfall events and preserve spatiotemporal dependency between multiple sites. This work evaluated an extension of the traditional Orthogonal Markov Chain (TOMC) model to reproduce the temporal structure of rainfall events in Florida, Nebraska, and California. A simulation of a hydrographic basin was also carried out from rainfall reproduced by a meteorological generator. The results show that (i) an extended temporal structure of the TOMC (EOMC) preserved the spatial correlation between observed and synthetic rainfall events; (ii) the EOMC used a smaller number of simulations to reproduce the observed frequencies of wet periods than those used by the TOMC to achieve similar precision; (iii) the use of EOMC-generated rainfall in the SWM...