New hydrological insights for the region: The hydrological data for The Judean Desert streams is partial to none. This study applied palaeoflood hydrology method, which analyzes sedimento-logical evidence of past large floods in two streams. One basin (N. Ze’elim, 250 km2) yield maximum palaeo-discharge of 900 m3s and the other (N. Rahaf, 55 km2) 1250 m3s (1.3 and 2.3 times larger than the maximum measured floods, respectively), for records of 500 and 5000 years, respectively. Combining these data with measured and historical data produced a palaeo- hydrological data-base of several hundred to thousands years long. These data updated the regional envelope curves for the maximum peak discharges. The improved FFA caused a decrease for the 100-year flood in the larger basin, from 1750 m3s for the systematic record only, to 760 m3s (43 %) for the combined records, and from 1260 m3s to 980 m3s in the other basin (77 %). The FFA for the systematic + historic data only, overestimated the frequency of the large floods due to their short and discontinuous records. The extension of the record with the palaeoflood data reduced the peak discharge values for different return periods and significantly enhanced FFA reliability. The study was funded by the Israel Water Authority, Grant No. 4501284533. Peer reviewed