Abstract—The aim of the paper is to analyze the characteristics of winter fog in terms of its trend and spatial-temporal variability over Indo-Gangetic plains. The study reveals that during last four and half decades (1971-2015), an alarming increasing trend in fog frequency has been observed during the winter months of December and January over the study area. The frequency of fog has increased by 118.4% during the peak winter months of December and January. It has also been observed that on an average central part of IGP has 66.29% fog days followed by west IGP with 41.94% fog days. Further, Empirical Orthogonal Function (EOF) decomposition and Mann-Kendall variation analysis are used to analyze the spatial and temporal patterns of winter fog. The findings have significant implications for the further research of fog over IGP and formulate robust strategies to adapt the fog variability and mitigate its effects. The decision by Delhi Government to implement odd-even scheme to restrict the use of private vehicles in order to reduce pollution and improve quality of air may result in increasing the alarming increasing trend of fog over Delhi and its surrounding areas regions of IGP. Keywords—Fog, climatology, spatial variability, temporal variability, empirical orthogonal function, visibility, Mann-Kendall test, variation point. I. INTRODUCTION HE influence of climate on our lives is all pervading as it is important factor in agriculture, commerce, industry, transport, tourism and many other important activities of daily life. Advance knowledge of information on climatology of meteorological parameters is of great demands from various users, planners, disaster management personals, tourism department etc. Reliable regional estimates of climate parameters are crucial for effective and efficient territorial management; thus there is a need to study these parameters and their changes over time, which includes temperature, humidity, rainfall and various other important meteorological events including fog. Over 70% of damage caused by natural phenomena is related to meteorological disasters, among which severe drought, floods, hail storms and fog are the most common. Fog is a hazardous weather phenomenon worldwide. The economic loss due to disruption in normal traffic schedules and accidents can be comparable to many natural disasters [1]. In addition, fog can cause discharge between power lines and interrupt electricity service. In recent years, some costly or Sanjay Kumar Srivastava is with the Dept. of Natural Resources, TERI University, 10 Institutional Area, Vasant Kunj, New Delhi, India and with the Indian Air Force (Corresponding author: phone: +91 9891910687; e-mail: Sk_khush@yahoo.co.in). Anu Rani Sharma and Kamna Sachdeva are with the Dept. of Natural Resources, TERI University. even catastrophic events in world have been caused by dense fog. Due to these known facts, it is unsurprising that much re- search has been carried out on fog all over the world. Fog studies through observations (Field observations and remote sensing), models, climatology, and statistical methods have resulted in many achievements [1]. As an example, the extent to which sea fog in the United Kingdom and United States has been studied is apparent in the review by Lewis et al [2]. Over India, the Indo-Gangetic Plains (IGP) in northern India experiences frequent fog episodes every winter (December–January) resulting from suitable meteorological and environmental conditions. Northern regions of India, Pakistan and Bangladesh experience severe fog conditions during winter season, which thoroughly disrupts human activities [3]. Visibility is reduced below 1000 m during fog, affecting public life. The negative impact of fog on human life has long been recognized. Every year, IGPs of India witness fog formation during the post-monsoon and winter months [4]. Several studies have attempted to examine various aspects of fog occurrence; however, these studies are limited to selective days over varied point locations [5]-[7]. Over recent decades, several authors have analyzed fog phenomenon in the northern part of India. Many researchers have studied various aspects of fog occurrence over Delhi and adjoining northern India during winter, however, there has not been any climatological study of the trend in fog formation over IGP India with ground base observation considering the latest data till 2015 [8], [9]. Over the Indo-Gangetic plains, the long duration of fog has been studied in detailed to know its climatic features. Presence of fog for more than 50% of the time during winter and an increase in fog frequency from 6.4 to 58% during the last four decades have also been reported in this region [10]. This alarming rise of fog events during the winter has been attributed to the rise in pollution levels and a gradual increasing trend in relative humidity. This alarming rise in fog frequency is another evidence of climate change which is a matter of serious concerned today for everyone all over the globe. Among the many disastrous consequences of climate change, an increase in frequency of fog occurrence over the IGP is also indeed an area of great concern for the inhabitant of this densely populated region of the world. The aim of this study is to analyze fog climatology, the trends of long-term changes of fog climatology and its spatial-temporal variability over the IGP, India using ground based observational data. Spatial and Temporal Variability of Fog Over the Indo-Gangetic Plains, India Sanjay Kumar Srivastava, Anu Rani Sharma, Kamna Sachdeva T World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:10, No:11, 2016 1042 International Scholarly and Scientific Research & Innovation 10(11) 2016 scholar.waset.org/1307-6892/10005967 International Science Index, Environmental and Ecological Engineering Vol:10, No:11, 2016 waset.org/Publication/10005967