Summary Kenya's Rift Valley has been undergoing rapid land cover change for the past two decades, which has resulted in ecological and hydrological changes. An effort is under way to quantify the timing and rate of these changes in and around the River Njoro watershed located near the towns of Njoro and Nakuru using remote sensing and geographic information system (GIS) methods. Three Landsat TM images, representing a 17‐year period from 1986 to 2003 in which the area underwent a significant land cover transition, were classified and compared with one another. Vegetation diversity and temporal variability, common to tropical and sub‐tropical areas, posed several challenges in disaggregating classified data into sub‐classes. An iterative approach for the resolving challenges is presented that incorporates unsupervised and supervised classification routines in coordination with knowledge‐based spatial analyses. Changes are analysed at three spatial scales ranging from the highly impacted and deforested uplands to the watershed and landscape scales. Land cover transitions primarily occurred after 1995, and included large forest losses coupled with increases in mixed small‐scale agriculture and managed pastures and degraded areas. These changes in cover type are highly spatially variable and are theorized to have significant impacts on ecological and hydrologic systems with implications for environmental sustainability.

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Sand dams have become popular in many parts of the arid world as a relatively cheap and effective water harvesting technology. Kenya is one of the countries with the highest number of such dams, with semi-arid Kitui County having become a major hub in recent decades. These sand dams are used for water storage in the beds of Kitui's seasonal rivers. The water is used for households and small-scale economic activities. Generally, sand dams are evaluated as very successful, but this paper shows that such success is not guaranteed. Field research conducted in Kitui County in October 2016 suggests that from 116 sand dams surveyed, about half did not have any water during the time of the assessment. This study assesses how various environmental factors affect sand dams' ability to supply water for community use during dry periods in Tiva River catchment in Kitui County. Most of the assessed environmental factors did not show consistent patterns to draw inferences on how they affect sand dams' ability to supply water, with the exception of rainfall amount, water indicating vegetation percentage of clay in a soil and stream orders. More overarching factors like agro-ecological zones and stream order do show a pattern of influence on dams' performance. These results have global significance due to the widespread use or plans to use of sand dams worldwide. There is a clear need to build a better understanding of sand dams performance to define more reliable sand dams' site identification criteria.

Thirty low-income Kenyan households using turbid river and relatively cleaner rain water participated in a 6 month in-home Biosand filter (BSF) performance study comprised of surveys and monthly monitoring of BSF influent and effluent water for turbidity and fecal coliforms (FC). River–river (influent–effluent) sample pairs (n = 155; 90% of observations) resulted in average BSF instantaneous FC and turbidity removals of 1.41 log10 (96.1%) and 32.5%, respectively. Cumulative distributions of influent and effluent quality demonstrated unambiguous improvement of river water but rain water improvement was limited and less reliable. Filter performance varied considerably within and across units. A hierarchical set of hypothesized factors affecting filter bacterial performance variability was assessed. BSF effluent FCs were positively correlated with influent (flush water) FCs and influent and effluent turbidity, and negatively correlated with turbidity applied to-date and days since maintenance. Interrupted use and moving the BSF negatively impacted effluent quality. Households with children age 6–10 collecting BSF filtered drinking water, or with more members, had higher effluent FCs. BSFs fed only river water performed better, on average, than mixed-source filters. Implications for BSF implementation in developing countries are discussed, including aqueous chemistry aspects of performance.