Macro rainwater harvesting techniques (Macro RWH) are getting more popular to overcome the problem of water scarcity in arid and semi-arid areas. Iraq is experiencing serious water shortage problem now despite of the presence of Tigris and Euphrates Rivers. RWH can help to overcome this problem. In this research, RWH was applied in Koya City in its districts, North West Iraq. Twenty-two basins were identified as the catchment area for the application of RWH technique. Watershed modeling system (WMS), based on Soil Conservation Service-curve number (SCS-CN) method, was applied to calculate direct runoff from individual daily rain storm using average annual rainfall records of the area. Two consecutive adjustments for the curve number were considered. The first was for the antecedent moisture condition (AMC) and the second was for the slope. These adjustments increased the total resultant harvested runoff up to 79.402 × 106 m3. The average percentage of increase of harvested runoff volume reached 9.28%. This implies that water allocation is of the order of 2000 cubic meter per capita per year. This quantity of water will definitely help to develop the area.
 N. A. Al-Ansari, “Management of Water Resources in Iraq: Perspectives and Prognoses,” Engineering, Vol. 5, No. 8, 2013, pp. 667-684.
 A. Hamdy, “Water Crisis and Food Security in the Arab World: The Future Challenges,” 2013.
 United Nations, “Water Resources Management White Paper,” United Nations Assistance Mission for Iraq, United Nations Country Team in Iraq, 2010, 20 p.
 FAO, “Water Profile of Iraq,” 2008.
 D. Prinz, “The Role of Water Harvesting in Alleviating Water Scarcity in Arid Areas,” Keynote Lecture, Proceedings of International Conference on Water Resources Management in Arid Regions, Vol. III, Kuwait, Kuwait Institute for Scientific Research, 23-27 March 2002, pp. 107-122.
 J. Chenoweth, P. Hadjinicolaou, A. Bruggeman, J. Lelieveld, Z. Levin, M. Lange, E. Xoplaki and M. Hadjikakoul, “Impact of Climate Change on the Water Resources of the Eastern Mediterranean and Middle East Region: Modeled 21st Century Changes and Implications,” Journal of Water Resources Research, Vol. 47, 2011, Article ID: W06506, pp. 1-18.
 K. Voss, J. Famiglietti, M. Lo, C. de Linage, M. Rodell and S. Swenson, “Groundwater Depletion in the Middle East from GRACE with Implications for Transboundary Water Management in the Tigris-Euphrates-Western Iran Region,” Water Resources Research, Vol. 49, No. 2, 2013, pp. 904-914. http://dx.doi.org/10.1002/wrcr.20078
 K. Shideed, T. Oweis and E. Mohammad, “Enhancing Agricultural Productivity through On-Farm Water-Use Efficiency: An Empirical Case Study of Wheat Production in Iraq,” ESCWA/SDPD, New York, 2003, p. 15.
 K. K. Gupta, J. Deelstra and K. D. Sharma, “Estimation of Water Harvesting Potential for a Semiarid Area Using GIS and Remote Sensing, Remote Sensing and Geographic Information System for Design and Operation of Water Resources System,” Proceedings of Information Symposium, Rabat, Vol. 242, 1997, pp. 53-62.
 S. Nasri, A. Jean, C. Christophe and B. Ronny, “Hydrological Processes in Macro Catchment Water Harvesting in the Arid Region of Tunisia: The Traditional System of Tabias,” Journal of Hydrological Sciences, Vol. 49, No. 2, 2004, pp. 261-272.
 T. Oweis, A. Hachum and J. Kijne, “Water Harvesting and Supplemental Irrigation for Improved Water Use Efficiency in Dry Areas,” International Water Management Institute, Colombo, 1999, 41 p.
 Th. M. Boers and J. Ben-Asher, “A Review of Rainwater Harvesting,” Agricultural Water Management, Vol. 5, No. 2, 1982, pp. 145-158.
 H. J. Finkel and M. Finkel, “Engineering Measures: Water Harvesting,” In: H. J. Finkel, M. Finkel and Z. Naveh, Eds., Semi-Arid Soil and Water Conservation, CRC Press, Inc., Boca Raton, 1986, pp. 93-101.
 K. Siegert, “Introduction to Water Harvesting. Some Basic Principles for Planning, Designand Monitoring,” In: FAO, Water Harvesting For Improved Agricultural Production. Expert Consultation, Cairo, 21-25 November 1994, pp. 9-23.
 S. Zakaria, N. A. Al-Ansari, S. Knutsson and M. EzzAldeen, “Rain Water Harvesting and Supplemental Irrigation at Northern Sinjar Mountain, Iraq,” Journal of Purity, Utility Reaction and Environment, Vol. 1, No. 3, 2012, pp. 121-141.
 S. Zakaria, N. A. Al-Ansari and S. Knutsson, “Rainwater Harvesting Using Recorded and Hypothetical Rainfall Data Scenarios,” Journal of Earth Sciences and Geotechnical Engineering, Vol. 3, No. 2, 2013, pp. 21-42.
 N. A. Al-Ansari, M. Ezz-Aldeen, S. Knutsson and S. Zakaria, “Water Harvesting and Reservoir Optimization in Selected Areas of South Sinjar Mountain, Iraq,” Journal of Hydrologic Engineering, 2013.
 A. H. Bakari, H. F. Mahoo and N. Hatibu, “Perormance of Maize under Gully Flow Supplementary Irrigation,” In: P. J. Makungu, H. F. Mahoo, V. C. K. Silayo and M. Mdemu, Eds., Proceedings of Tanzania Society of Agricultural Engineers, Vol. 8, 1998, pp. 20-42.
 J. W. Gowing, H. F. Mahoo, O. B. Mzirai and N. Hatibu, “Review of Water Harvesting Techniques and Evidence for Their Use in Semi-Arid Tanzania,” Tanzania Journal of Agricultural Science, Vol. 2, No. 2, 1999, pp. 171-180.
 H. J. Bruins, M. Evenari and U. Nessler, “RainwaterHarvesting Agriculture for Food Production in Arid Zones the Challenge of the African Famine,” Applied Geography, Vol. 6, No. 1, 1986, pp. 13-32.
 P. Fox and J. Rockstrom, “Supplemental Irrigation for DrySpell Mitigation of Rainfed Agriculture in the Sahel,” Agricultural Water Management, Vol. 61, No. 1, 2003, pp. 29-50.
 N. Hatibu, M. D. B. Young, J. W. Gowing, H. F. Mahoo and O. B. Mzirai, “Developing Improved Dryland Cropping Systems for Maize in Semi-Arid Tanzania. Part 1: Experimental Evidence for the Benefits of Rainwater Harvesting,” Experimental Agriculture, Vol. 39, No. 3, 2003, pp. 279-292.
 K. E. Motsi, E. Chuma and B. B. Mukamuri, “Rainwater Harvesting for Sustainable Agriculture in Communal Lands of Zimbabwe,” Physics and Chemistry of the Earth, Vol. 29, No. 15-18, 2004, pp. 1069-1073.
 J. Barron and G. Okwach, “Run-Off Water Harvesting for Dry Spell Mitigation in Maize (Zea mays L.): Results from On-Farm Research in Semi-Arid Kenya,” Agricultural Water Management, Vol. 74, No. 1, 2005, pp. 1-21.
 F. Liu, Y. Wu, H. Xiao and Q. Gao, “Rainwater-Harvesting Agriculture and Water Use Efficiency in Semi-Arid Regions in Gansu Province, China,” Outlook on Agriculture, Vol. 34, No. 3, 2005, pp. 159-165.
 K. O. Adekalu, J. A. Balogun, O. B. Aluko, D. A. Okunade, J. W. Gowing and M. O. Faborode, “Runoff Water Harvesting for Dry Spell Mitigation for Cowpea in the Savannah Belt of Nigeria,” Agricultural Water Management, Vol. 96, No. 11, 2009, pp. 1502-1508.
 N. Hatibu and H. Mahoo, “Rainwater Harvesting Technologies for Agricultural Production: A Case for Dodoma, Tanzania,” In: P. G. Kaumbutho and T. E. Simalenga, Eds., Conservation Tillage with Animal Traction. A Resource Book of the Animal Traction Network for Eastern and Southern Africa, ATNESA, Harare, 1999, 173 p.
 J. Rockstrom, L. Karlberg, S. P. Wani, J. Barron, N. Hatibu, T. Oweis, A. Bruggeman, J. Farahani and Q. Zhu, “Managing Water in Rainfed Agriculture. The Need for a Paradigm Shift,” Agricultural Water Management, Vol. 97, 2010, pp. 543-550.
 T. Oweis and A. Hachum, “Water Harvesting for Agriculture in Dry Areas,” CRC Press, Balkema, 2012, p. 57.
 S. L. Neitsch, J. G. Arnold, J. R. Kiniry and J. R. Williams, “Soil and Water Assessments Tool Theoretical Documentation,” 2005, p. 102.
 ASCE, “ASCE/EWRI Curve Number Hydrology Task Committee,” In: R. H. Hawkins, T. J. Ward, E. W. Donald and J. A. Van Mullem, Eds., Curve Number Hydrology: State of the Practice, American Society of Civil Engineers, Reston, 2009, 116 p.
 H. Mohammed, “Water Harvesting in Erbil Governorate, Kurdistan Region, Iraq. Detection of Suitable Sites Using Geographic Information System and Remote Sensing,” Master Thesis, Lund University, 2013, 13 p.
 S. Zakaria, N. A. Al-Ansari, Y. Mustafa, S. Knutsson, P. Ahmad and B. Ghafour, “Rainwater Harvesting at Koysinjaq (Koya), Kurdistan Region, Iraq,” Journal of Earth Sciences and Geotechnical Engineering, 2013.