Science and Education Publishing American Journal of Water Resources 2333-4819 3 5 2015 11 3 Water Balance and Climatic Classification of a Tropical City Delhi - India 124 146 EN Yashvant Das Research and Modeling Division, AIR Worldwide India Private Limited, Hyderabad, India AJWR2015351 10.12691/ajwr-3-5-1 2015 7 8 2015 8 15 2015 11 1 Water balance is a concept used to understand the availability and the overall state of water resources in a hydrological system which forms the basis of the principle of mass conservation applied to exchanges of water and ensures the magnitudes of the various water exchange processes. Urbanization results in tremendous land cover change dynamics along with subsequent changes in the water and energy balance relationship of earth-atmospheric system. In this paper an attempt has been made to illustrate the small-scale spatial and temporal characteristics of the water balance components and to classify the climate of the tropical city Delhi through the application of the water balance model. In the modeling processes, the potential evapotranspiration (PE) was computed using Thornthwaite's method and compared with the Penmen's for the representative station. The complete water balance is evaluated by following an elegant book-keeping procedure given by Thornthwaite. Thornthwaite and Mather's modified moisture index scheme, which is widely used and accepted by scientific community, is adopted to classify the climate of Delhi. According to the moisture indices, the entire city falls under the semiarid category of climate, except at a location, where it shifted to dry sub humid. This could be a freak occurrence.