Korana, Glina and Sunja to the northwest, the Adriatic watersheds of the Lika, Zrmanja and Cetina to the southwest, the watershed of the Cetina to the south and the watersheds of the Vrbas and Jablanica to the east. The shape of the watershed itself is very irregular, but roughly triangular. Due to strong karst influence in the area, the watershed is poorly developed with few large surface streams. The karstification coefficient for the entire watershed is 0.244, which means that 24.4% of the surface area in the watershed lacks proper surface streams and drainage. The karstification coefficient up to Bihać is 0.43, up to Novi Grad 0.28 and up to Kostajnica 0.26. The average air temperature in the area of the watershed is , and the average amount of annual rainfall is . The watersheds of the Una and the watersheds of the Korana and Glina are often grouped together for analytical purposes in Bosnia and Herzegovina. Discharge The Una river has an average discharge of at its mouth, with a minimal discharge of . There are relatively small differences in the average monthly discharges (the driest month August has 37% of average yearly discharge while the wettest month April has 155%) and minimal daily and monthly discharges also show a very small difference. Low discharges last a relatively long time and high discharges appear quickly due to sudden rainfall and snowmelt and last a comparatively short amount of time. High discharges and water levels are present in April and December, and low discharges in August and January. There are multiple measuring stations in Bosnia and Herzegovina on the Una, and their data is show in the tables below Tributaries The Una river has a relatively weakly developed network of tributaries, owing to its karst geology. Most of the tributaries are shorter rivers, albeit with strong sources and relatively large discharges. There is also a number of karst springs located directly at the main channel of the river. The right tributaries of the river are the Krka, Unac, Krušnica, Vojskova and Sana rivers, and the left tributaries are the Dobrenica, Drobinica, Klokot and Baštra rivers. Sana The Sana river is the longest and most important tributary of the Una river, with a watershed size of and average discharge of over . Its source is located under Lisina mountain, 420 m above sea level. The longest headwater of the Sana is