Assessing the Potential for Rooftop Rainwater Harvesting from Large Public Institutions

Abstract

As in many other cities, urbanization coupled with population growth worsens the water supply problem of Addis Ababa, Ethiopia, with a water supply deficit of 41% in 2016. To investigate the potential contribution of rooftop rainwater harvesting (RWH) from large public institutions, 320 such institutions were selected and grouped into 11 categories, from which 25–30% representative 588 rooftops were digitalized and the potential RWH volume computed based on a ten-year rainfall dataset. When comparing the resulting RWH potential with the water consumption, up to 2.3% of the annual, potable water supply can be provided. If reused only within one’s own institution, the self-sufficiency varies from 0.9 to 649%. Non-uniform rainfall patterns add uncertainty to these numbers, since the size of the storage tank becomes critical for coverage in the dry season from October to May. Despite the low replacement potential at the city level, RWH from large institutions will enable a significant volume of potable water to be transferred to localities critically suffering from water shortage. Further, large institutions may demonstrate how RWH can be practiced, thus acting as a frontrunner for the dissemination of RWH to other types of rooftops. To narrow the water supply gap, considering rooftop RWH as an alternative water supply source is recommended. However, the present study assumed that financial constraints to install large sized storage tanks are considered as a possible challenge. Thus, future research is needed to investigate the cost-benefit balance along with the invention of a cheap storage tank as they may affect the potential contribution of RWH from rooftops.

Assessment of Rainwater Harvesting Potential from Roof Catchments through Clustering Analysis

“…As a preliminary step to evaluating the potential water savings, rainwater capture and harvesting potential (RCHP) must be calculated. To calculate this, the Formula (1) is applied [28,29].…”

“…Likewise, in areas with considerable inter-annual variation, the RCHP is estimated for different rainfall scenarios [27]. Other studies give greater importance to seasonal rainfall variability for analyzing its impact on water-saving potential since seasonality affects the performance of RWHS [28,29]. Thirdly, to assess the runoff coefficient (RC) most research uses a fixed value without considering the influence of the rooftop slope and material.…”

“…These conditions determine that RWHS in arid environments should be designed as an alternative water supply for non-essential uses, since the variability of precipitation reduces reliability. It should be also borne in mind that the irregularity and scarcity of precipitation are two factors habitually related to a lower RWHS performance [28,29]. For these reasons, in semiarid environments, it is crucial to consider the main parameters that affect the performance of the RWHS, which are population density and roof area [32,36].…”

Is Rainwater Harvesting Sufficient to Satisfy The Emergency Water Demand for The Prevention of COVID-19? The Case of Dilla town, Southern, Ethiopia

“…To assess rainwater harvesting potential in the selected institutions in Dilla Town the average roof size was adopted from similar institutions in Addis Ababa [31]. We took the assumption that the roof sizes of the institutions in the two cities would be proportional.…”

Development of dual water supply using rooftop rainwater harvesting and groundwater systems

“…In Seoul, South Korea, Mun and Han [21] estimated the collection efficiency of rainwater from a building rooftop of 0.8. A runoff coefficient of 0.85 was employed in a study carried out by Adugna et al [22] to account for evaporation loss and possible first flush diversion. Overall, the actual volume of calculated harvested rainwater ranged from 6.4 to 12.5 m 3 , while the observed volume of harvested rainwater in the storage tank ranged from 5.6 to 11.5 m 3 ( Table 2).…”