Title: Separation of large scale water storage patterns over Iran using GRACE, altimetry and hydrological data
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Publication by: Forootana et al
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Abstract: Extracting large scale water storage (WS) patterns is essential for understanding the hydrological cycle and improving the water resource management of Iran, a country that is facing challenges of limited water resources. The Gravity Recovery and Climate Experiment (GRACE) mission offers a unique possibility of monitoring total water storage (TWS) changes. An accurate estimation of terrestrial and surface WS changes from GRACE-TWS products, however, requires a proper signal separation procedure. To perform this separation, this study proposes a statistical approach that uses a priori spatial patterns of terrestrial and surface WS changes from a hydrological model and altimetry data. The patterns are then adjusted to GRACE-TWS products using a least squares adjustment (LSA) procedure, thereby making the best use of the available data. For the period of October 2002 to March 2011, monthly GRACE-TWS changes were derived over a broad region encompassing Iran. A priori patterns were derived by decomposing the following auxiliary data into statistically independent components: (i) terrestrial WS change outputs of the Global Land Data Assimilation System (GLDAS); (ii) steric-corrected surface WS changes of the Caspian Sea; (iii) that of the Persian and Oman Gulfs; (iv) WS changes of the Aral Sea; and (v) that of small lakes of the selected region. Finally, the patterns of (i) to (v) were adjusted to GRACE-TWS maps so that their contributions were estimated and GRACE-TWS signals separated. After separation, our results indicated that the annual amplitude of WS changes over the Caspian Sea was 152 mm, 101 mm over both the Persian and Oman Gulfs, and 71 mm for the Aral Sea. Since January 2005, terrestrial WS in most parts of Iran, specifically over the center and northwestern parts, exhibited a mass decrease with an average linear rate of ∼ 15 mm/yr. The estimated linear trends of groundwater storage for the drought period of 2005 to March 2011, corresponding to the six main basins of Iran: Khazar, Persian and Oman Gulfs, Urmia, Markazi, Hamoon, and Srakhs were -6.7, -6.1, -11.2, -9.1, -3.1, and -4.2 mm/yr, respectively. The estimated results after separation agree fairly well with 256 in-situ piezometric observations. Keywords: GRACE-TWS, Signal separation, Independent components, Terrestrial and surface water storage, Groundwater, Iran
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Abstract: Extracting large scale water storage (WS) patterns is essential for understanding the hydrological cycle and improving the water resource management of Iran, a country that is facing challenges of limited water resources. The Gravity Recovery and Climate Experiment (GRACE) mission offers a unique possibility of monitoring total water storage (TWS) changes. An accurate estimation of terrestrial and surface WS changes from GRACE-TWS products, however, requires a proper signal separation procedure. To perform this separation, this study proposes a statistical approach that uses a priori spatial patterns of terrestrial and surface WS changes from a hydrological model and altimetry data. The patterns are then adjusted to GRACE-TWS products using a least squares adjustment (LSA) procedure, thereby making the best use of the available data. For the period of October 2002 to March 2011, monthly GRACE-TWS changes were derived over a broad region encompassing Iran. A priori patterns were derived by decomposing the following auxiliary data into statistically independent components: (i) terrestrial WS change outputs of the Global Land Data Assimilation System (GLDAS); (ii) steric-corrected surface WS changes of the Caspian Sea; (iii) that of the Persian and Oman Gulfs; (iv) WS changes of the Aral Sea; and (v) that of small lakes of the selected region. Finally, the patterns of (i) to (v) were adjusted to GRACE-TWS maps so that their contributions were estimated and GRACE-TWS signals separated. After separation, our results indicated that the annual amplitude of WS changes over the Caspian Sea was 152 mm, 101 mm over both the Persian and Oman Gulfs, and 71 mm for the Aral Sea. Since January 2005, terrestrial WS in most parts of Iran, specifically over the center and northwestern parts, exhibited a mass decrease with an average linear rate of ∼ 15 mm/yr. The estimated linear trends of groundwater storage for the drought period of 2005 to March 2011, corresponding to the six main basins of Iran: Khazar, Persian and Oman Gulfs, Urmia, Markazi, Hamoon, and Srakhs were -6.7, -6.1, -11.2, -9.1, -3.1, and -4.2 mm/yr, respectively. The estimated results after separation agree fairly well with 256 in-situ piezometric observations. Keywords: GRACE-TWS, Signal separation, Independent components, Terrestrial and surface water storage, Groundwater, Iran
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Title: Evaluating the uncertainty in gridded rainfall datasets over Eastern Africa for assessing the model performance and understanding climate change
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Title: Linkages between the Indian Ocean Dipole and East African Seasonal Rainfall Anomalies
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Publication by: ZABLONE OWITI LABAN .A. OGALLO, JOSEPH MUTEMI
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Abstract: This study was designed to understand the nature of the relationship between the Indian Ocean Dipole (IOD) index and seasonal rainfall in East Africa using statistical approaches. The statistical methods used in this study include correlation, regression and composite analyses. Results from the analyses suggested that the pattern in Sea Surface Temperature (SST) anomalies manifested during the IOD events have strong signals on the regional climate system during the October to December rainfall season. The study has demonstrated that some of the extreme rainfall conditions over East Africa were associated with positive and negative IOD phases. The linkages were strong during El Niño/La Niña years. Such information will help to improve monitoring, prediction and early warning of extreme rainfall events over east Africa to reduce the vulnerability of the society of the region to negative impacts of extreme rainfall events that are common in the region.
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Abstract: This study was designed to understand the nature of the relationship between the Indian Ocean Dipole (IOD) index and seasonal rainfall in East Africa using statistical approaches. The statistical methods used in this study include correlation, regression and composite analyses. Results from the analyses suggested that the pattern in Sea Surface Temperature (SST) anomalies manifested during the IOD events have strong signals on the regional climate system during the October to December rainfall season. The study has demonstrated that some of the extreme rainfall conditions over East Africa were associated with positive and negative IOD phases. The linkages were strong during El Niño/La Niña years. Such information will help to improve monitoring, prediction and early warning of extreme rainfall events over east Africa to reduce the vulnerability of the society of the region to negative impacts of extreme rainfall events that are common in the region.
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Title: ASSESSMENT OF THE SKILL/ACCURACY OF THE REGIONAL SPECTRAL MODEL (RSM) OVER THE GHA REGION
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Publication by: Franklin J. Opijah, Joseph M. Mutemi
Publication Date : June 2009
Abstract: As a whole, Eastern Africa, including the Greater Horn of Africa (GHA) that encompasses the Intergovernmental authority on Development (IGAD) countries together with East Africa region, the Western Indian Ocean, and North-eastern parts of the Southern Africa Development Corporation (SADC), has varied weather and climate controls. The objective of this research report was to assess the performance of the Regional Spectral Model (RSM) in downscaling Echam model outputs over the GHA region, with respect to rainfall and temperature prediction.
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Publication Date : June 2009
Abstract: As a whole, Eastern Africa, including the Greater Horn of Africa (GHA) that encompasses the Intergovernmental authority on Development (IGAD) countries together with East Africa region, the Western Indian Ocean, and North-eastern parts of the Southern Africa Development Corporation (SADC), has varied weather and climate controls. The objective of this research report was to assess the performance of the Regional Spectral Model (RSM) in downscaling Echam model outputs over the GHA region, with respect to rainfall and temperature prediction.
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