Rainfall is one of the key elements in establishing climate, along with temperature. It can have a significant impact on the management of agriculture, ecosystems, and water resources due to its spatial distribution and changing properties 1. One of the biggest problems of our time is climate change. A long-term shift in the typical weather patterns is referred to as climate change. The impact of climate change on weather and extreme events is becoming more well-recognized. In the 20th century, there has been a dramatic change in the patterns of rainfall over the world 2.

The global variability of precipitation in terms of both space and can be obtained from infrared sensor readings on passive microwave sensors carried on board geostationary satellites by the newly operational radars on board and the polar-orbiting satellites the TRMM satellite and its successors. TRMM was a research satellite that functioned from 1997 to 2015. Its purpose was to improve our understanding of the distribution and variability of precipitation in the tropics as part of the water cycle in today's climate system. As an extension and enhancement of the TRMM data, the Global Precipitation Measurement (GPM) Core Satellite was launched in February 2014.

The major threats to agriculture and food security are changing weather patterns such as less predictable seasons more frequent rainfall events and prolonged droughts (IPCC 2001) 3. The most important factor that affects Indian agriculture is the monsoon because 70% of it is dependent on the monsoon 4. Global warming is one of the reasons for the occurrences of heavy rainfall events nowadays (Goswami et al 2006 5; Turner and Annamalai 2012). Rainfall is the main source of river flow in India. Extreme rainfall variability thus increases the frequency of extreme hydrological events like droughts and floods. The temporal and spatial variability of rainfall is crucial from both scientific and economic viewpoints 6, 7, 8, 9, 10.

The study area is located in the Western Ghats of Karnataka and is characterized as one of the biodiversity hotspots in the world. The climate and topography of the region support a wide variety of plants and animal species. But the region is now undergoing rapid transformation. The high deforestation rate, illegal hunting, hydroelectric projects, mining, and extraction of forest resources is altering the region and would seriously affect the variability of rainfall in the study region. Similarly, Agriculture is a major economic activity in the river basin. Rainfall variability directly impacts crop yields and influences decisions related to crop selection, planting times, and irrigation needs. The study helps the farmers to optimize their practices based on the expected rainfall patterns. Further, the health of aquatic ecosystems in the Tunga River basin is closely tied to the availability of water. Variability in rainfall can affect river flow, water levels, and overall ecosystem health. Understanding these variations is vital for preserving biodiversity and maintaining ecological balance in the study area. Understanding the variability in rainfall helps in managing water resources effectively. In this context, this study aims to find out the variability of rainfall in the Tunga River basin, Karnataka using Remote Sensing and GIS techniques to understand the distribution pattern of rainfall within the study basin for sustainable water management.

Tunga is a river that flows through the state of Karnataka, India. The river originates in the western ghats and flows through two states of Karnataka, Chikmagalur and Shivamogga. Rivers Tunga and Bhadra are the principal tributaries of Krishna in Karnataka along with other tributaries like Ghataprabha, Mala Prabha, and Bhima. Tunga River Basin is located between 13˚24′ N to 14˚03′ and 75˚07′ E to 75˚67′ E having an aerial extent of 2722 sq. km. It flows through the state of Karnataka. The study area map is shown in Figure 1.

The river originates in the Western Ghats on Varaha Parvata hill, Ganga Moola. Three important rivers, the Tunga, the Bhadra, and the Nethravathi have their origin here. The river flows through two districts of Karnataka- Chikmagalur and Shivamogga. It has a length of 147 km. The river merges with Bhadra at Koodli, a small village near Shivamogga. From here the river is known as Tungabhadra. The river Tungabhadra flows eastwards and joins the Krishna River in Andhra Pradesh.

Recognizing the potential ramifications of any alterations in the rainfall patterns, this research aimed to comprehensively examine and understand the variability of precipitation in the Tunga River basin in Karnataka, which serves as a critical catchment within the Western Ghats. The study utilized TRMM 3B43 monthly data for a thorough investigation into the patterns and trends of rainfall variability. The study revealed distinct spatial and temporal variations, emphasizing the need for a detailed understanding of these dynamics for effective water resource planning and management. Notably, the southern part of the basin consistently experienced higher rainfall across all seasons, with a spatial trend observed from southwest to northeast. The correlation between spatial variability and terrain elevation highlighted the influence of topography on precipitation, with elevated areas in the southern part receiving more rainfall compared to lower elevation areas in the northern eastern parts. Temporal variability analysis further emphasized the dominance of the monsoon season in terms of rainfall, with July identified as the peak month. The persistence of low rainfall during the winter season throughout the studied years underscores the seasonal variation of precipitation in the Tunga River basin.

The findings of the study not only contribute to the scientific understanding of rainfall variability but also hold practical significance for the states reliant on the Tunga River and its tributaries. The awareness generated through this research assists in informed decision-making in water resource planning, especially in the face of potential modifications to rainfall patterns that could significantly impact the socio-economic and ecological fabric of the region. As climate change continues to pose challenges, this study serves as a foundation for developing adaptive strategies and sustainable management practices in the Tunga River basin.