Journal of Applied and Industrial Sciences, 2013, 1 (5): 20-23, ISSN: 2328-4595 (PRINT), ISSN: 2328-4609 (ONLINE) Research Article 6 Abstract- this study was carried out at five sites in Khartoum State namely: Al Kadaru and Al Safia in Bahri town; Wad Nubawi and Al Salha in Omdurman town; and Al Riyadh in Khartoum town. The objective of the study was to determine the relationship between relative humidity (RH) and dew point temperature (Td) in Khartoum State. Td was calculated from actual readings of air temperature (T) and RH using an online calculator. The data of air temperature and RH were recorded throughout a calendar year (December 2010 to November 2011). The readings were made in the bare land at approximately 1.5 - 2 meters height which represents the environment in which the human beings live. Pooled data from the five sites were used to calculate Td for Khartoum State. The data on RH and Td were analyzed using the computer packages SPSS 18.0 for Windows and Microsoft Excel version 7. Trend graphs of RH and Td against months were drawn and scatter plots of RH against Td were fitted. Six regression equations were obtained using the curve estimation procedure to determine the relationship between RH and Td in for the five sites and for Khartoum State from the pooled data of the five sites. All the relationships between RH and Td were exponential with significant coefficients of determination (R 2 ). Index Terms- Dew point temperature, air temperature, relative humidity, exponential relationship I. INTRODUCTION EW point temperature (Td) is the temperature at which the air becomes saturated with water vapor [1]; it is a great weather tool in forecasting the rain, frost and fog formation as well as the probability of thunderstorms during summer. Td is different from the relative humidity (RH) even though both are prospective tools in weather forecast and are used to express the amount of moisture in the air. Td is the temperature to which air must be cooled for condensation to occur or it indicates how much moisture is in the air, whereas RH is a percentage that indicates how saturated the air is [2]. In other words, the higher the dew point is, the more moisture is in the air and vice versa. In addition to that: if the dew point *Corresponding author E- mail: hisham-7777@hotmail.com The authors acknowledge with gratitude the assistance rendered to them by Mr. El Mughiera M. Ibrahim (CNRES) during data logging. is closer to the actual air temperature, the air becomes more and more humid; when the temperature is closer to the Td, the RH approaches 100% leading to muggy conditions, and it can never be higher than the air temperature [2] [3]. Dew point can also be used to give a very rough estimate of how low the temperature will drop during the night [4]. Although Td rarely rises above 80% even in the topical areas; in Chicago, United States, Td ranged from 80 - 83 o C all time, whereas the world’s highest dew point was 84 degrees observed along the Ethiopian coast of the Red Sea [5]. II. STUDY SITE AND METHODOLOGY Air temperature (°C) and RH (%) data for this study were collected from five sites in Khartoum State: namely, Al Kadaru, Al Safia, Wad Nubawi, Al Salha, and Al Riyadh. Anemometer Pen – Model 800047 was used in RH data logging and Digital Oxygen and Temperature-Meter Model- 800047 was used in temperature data logging. Spontaneous air temperature and RH readings were taken simultaneously at an approximate height of 1.5 to 2.0 meters on the assumption that it is the height at which human beings live [6]. The readings were made every other hour from 8.00 am to 6.00 pm during the period of December 2010 to November 2011. Most days of measurements were sunny without clouds except during the autumn (August and September). Monthly means of the collected data were used for calculating Td for the five sites. Pooled data from the five sites were used to represent Khartoum State. Td was calculated from actual readings of air temperature (T) and RH using an online calculator [7]. The data on RH and Td were analyzed using the computer packages SPSS 18.0 for Windows and Microsoft Excel version 7. Trend graphs of RH and Td against months were drawn and scatter plots of RH against Td were fitted. Six regression equations were obtained using the curve estimation procedure to determine the relationship between RH and Td in for the five sites and for Khartoum State from the pooled data of the five sites. III. RESULTS Trends of RH and Td against months of the study period for the five sites showed a gradual decrease in RH and Td in winter months (November - April) where minimal monthly means of RH and Td ranged from 10% to 32% and -4 o C to 12 o C respectively. In summer months (April - October) there was a slight increase in HR and Td during May, June and July; followed by a sharp rise in RH and Td in August, followed by The Relationship between Relative Humidity and the Dew point Temperature in Khartoum State, Sudan Tawhida A. Yousif 1 and Hisham M. M. Tahir 2 * 1 Freelance Researcher (E -mail: tawhida11@hotmail.com). 2 Associate Professor at the College of Natural Resources and Environmental Studies, University of Bahri, Sudan (Received October 22, 2013; Accepted December 16, 2013) D