Kazi Ali Tamaddun

Potential of rooftop rainwater harvesting to meet outdoor water demand in arid regions

The feasibility of rooftop rainwater harvesting (RRWH) as an alternative source of water to meet the outdoor water demand in nine states of the U.S. was evaluated using a system dynamics model developed in Systems Thinking, Experimental Learning Laboratory with Animation. The state of Arizona was selected to evaluate the effects of the selected model parameters on the efficacy of RRWH since among the nine states the arid region of Arizona showed the least potential of meeting the outdoor water demand with rain harvested water. The analyses were conducted on a monthly basis across a 10-year projected period from 2015 to 2024. The results showed that RRWH as a potential source of water was highly sensitive to certain model parameters such as the outdoor water demand, the use of desert landscaping, and the percentage of existing houses with RRWH. A significant difference (as high as 37.5%) in rainwater potential was observed between the projected wet and dry climate conditions in Arizona. The analysis of the dynamics of the storage tanks suggested that a 1.0–2.0 m3 rainwater barrel, on an average, can store approximately 80% of the monthly rainwater generated from the rooftops in Arizona, even across the high seasonal variation. This interactive model can be used as a quick estimator of the amount of water that could be generated, stored, and utilized through RRWH systems in the U.S. under different climate conditions. The findings of such comprehensive analyses may help regional policymakers, especially in arid regions, to develop a sustainable water management infrastructure.

Multi-Scale Correlation Analyses between California Streamflow and ENSO/PDO

El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) are two of the most important climate indices that influence the western U.S. hydrology significantly. This study evaluated how these two indices have influenced California streamflow over the years and determined their correlation at multiple time-scales. Data were obtained from 14 unimpaired streamflow stations of California for a study period of 63 years (i.e., 1951 to 2013). The concept of continuous wavelet transform was applied to observe the variance in each time-series at multiple time-scale bands over the years. The correlation was found to be higher in the latter half of the study period. ENSO showed a higher correlation with California streamflow compared to PDO across the study period. The results of this study can be of assistance in determining the relationship between Pacific SST fluctuation and California streamflow. The findings may help understand the recent California drought as well.

Precipitation and Indian Ocean Climate Variability-A Case Study on Pakistan

The study evaluated the relationship between two climate variability indicators – seasurface temperature (SST) and 500-mbar geopotential height (HGT/Z500) – and the monsoonal precipitation pattern of Pakistan. Data from 30 precipitation gauges were obtained and were analyzed over a period of 35 years from 1980 to 2014. Singular-valued decomposition (SVD) technique was used to determine the association of previous year’s SST and HGT with the current year’s monsoonal precipitation. The results indicated that the association of SST and HGT with precipitation varied depending on the lead-times selected. Multiple regions of the North Indian Ocean were identified that showed significant association in affecting Pakistan’s precipitation. The long term trend and abrupt shift patterns of precipitation were also evaluated across the selected gauges to determine the generic change patterns. The findings of the study can be useful predictors of forecasting models for water management in Pakistan.

Spectral Analysis of Streamflow for Continental U.S.A.

Evaluating streamflow changes is one of the most important tasks in hydrology, which provides significant insight regarding the trends that occur in streamflow due to climate variability and change. This study focused on investigating the presence of gradual changes (trends) and abrupt changes (shifts) in 240 unimpaired streamflow stations across the continental United States. Discrete Wavelet Transform (DWT) was used as the trend detection method, which is one of the techniques used in Spectral Analysis. The changes in streamflow in water-year were analyzed along with three dyadic scales (1year, 2 years and 4 years) for 60 years i.e., 1951-2010. The non-parametric Mann-Kendall test was used to identify the trends, whereas the non-parametric Pettitt test was used to identify the shifts. The results showed a significant increase in streamflow in the Northeast and Midwest (Upper Mississippi and Ohio) regions and a decrease in the Pacific Northwest region. The central regions, especially Missouri, had mixed results with a propensity towards increasing trends. The southern U.S. regions did not show any overall significant trends. The shifts were found to be more spatially dispersed and were in agreement with the gradual trends. More stations showed trends and shifts with increasing time scales, which implies the presence of periodic occurrences at 4 years or higher. The presence of persistence was also observed to increase with the increasing time-scales. The results from the current study may assist water managers to efficiently plan and manage the water resources under changing climatic conditions.