THE AVAILABILITY OF LIQUID WATER AT THE MARTIAN SURFACE IS STRONGLY AFFECTED BY MARTIAN CLIMATE. ON PRESENT DAY MARS WHERE ATMOSPHERIC PRESSURE IS 6 MBAR WATER BOILS AT 273 K AND FREEZES BELOW THIS TEMPERATURE (MURPHY AND KOOP 2005). IT IS WELL ACCEPTED THAT THE CLIMATE OF EARLY MARS (&GT;3.5 GA) WAS VERY DIFFERENT ENABLING THE FORMATION OF ABUNDANT FLUVIAL FEATURES AND LAKES (E.G. MANGOLD ET AL. 2008 FASSETT AND HEAD 2005) AND HYDROUS MINERALS THAT REQUIRE TEMPERATURES ABOVE FREEZING (E.G. BISHOP ET AL. 2018). A THICKER CO2 ATMOSPHERE SINCE LOST WITH ADDITIONAL GREENHOUSE GASSES (E.G. RAMIREZ 2017 WORDSWORTH ET AL. 2017) IS PROPOSED TO EXPLAIN THIS WARMING. HOWEVER THERE IS INCREASING EVIDENCE THAT CONDITIONS ENABLING THE STABILITY OF SURFACE LIQUID WATER EXTENDED LATER INTO MARS HISTORY (E.G. KITE ET AL. 2019 WILSON ET AL. 2016 DICKSON ET AL. 2009) POTENTIALLY EXTENDING MARS HABITABILITY INTO THE AMAZONIAN (E.G. KITE ET AL. 2017). THE GEOMORPHIC ROLE OF LATER SURFACE WATER CAN BE USED TO CONSTRAIN HOW MUCH WATER WAS PRESENT WHERE IT CAME FROM AND HOW LONG IT REMAINED AT THE SURFACE. WET EVENTS ON MARS SINCE THE MAIN LATE NOACHIAN AND EARLY HESPERIAN VALLEY NETWORK (VN) FORMING FLUVIAL ACTIVITY ARE RECORDED BY YOUNG ALLUVIAL FANS (KITE ET AL. 2019 GRANT AND WILSON 2011) FRESH SHALLOW VALLEYS (FSVS) (WILSON ET AL. 2016 MANGOLD 2012) AND SMALL EXIT BREACH CRATERS OR POLLYWOGS (WILSON ET AL. 2016). POLLYWOGS CANNOT BE DATED USING CRATER STATISTICS DUE TO THEIR SMALL SIZE BUT THEIR PRESERVED CRATER RIMS INDICATES THAT THEY POST-DATE PERIODS OF INTENSE FLUVIAL ACTIVITY DURING THE LATE NOACHIAN AND EARLY HESPERIAN (WILSON ET AL. 2016). POLLYWOGS ARE CRATERS WITH ONE OR MORE VALLEYS LEADING OUTWARDS FROM THE CRATER RIM BUT NO INLET VALLEYS (WILSON ET AL. 2016). THESE OUTLET CHANNELS ARE THOUGHT TO FORM DURING OVERFLOW OF WATER FROM WITHIN THE CRATER. THE PROCESS(ES) THAT FORM POLLYWOGS WERE NOT LOCALIZED TO ONE PART OF THE MARS SURFACE BUT WERE ABLE TO OCCUR IN MULTIPLE LOCATIONS. WE WILL OBTAIN A LOWER LIMIT ON THE VOLUME OF WATER AND NUMBER OF OUTFLOW EVENTS REQUIRED TO PRODUCE OBSERVED POLLYOG OUTFLOW DEPTHS USING A NEW BREACH EROSION MODEL THAT COUPLES LAKE DRAINING AND SEDIMENT TRANSPORT. WE WILL COMPARE THE RESULTS OF OUR BREACH EROSION MODEL IN WITH MEASUREMENTS FROM 7 NEW POLLYWOG DEMS TO CONSTRAIN THE MINIMUM NUMBER OF CRATER OVERSPILL EVENTS. MODELLING CHANNEL BREACH EROSION PROCESSES AND THE FREEZING/EVAPORATION OF WATER ON THE PAST MARTIAN SURFACE ADDRESSES THE SOLAR SYSTEM WORKINGS GROUP INTEREST IN THE EVOLUTION AND MODIFICATION OF SURFACES PARTICULARLY HOW THE MARTIAN HYDROSPHERE AND CRYOSPHERE INTERACTED WITH MARS SURFACE DURING THE DRIER PARTS OF ITS HISTORY (SECTION 1 OF C.3 SOLAR SYSTEM WORKINGS 2019). THIS IS ALSO RELEVANT TO MEPAG GOAL II INVESTIGATION C2.2. WE WILL CARRY OUT TIME-DEPENDENT ENERGY BALANCE MODELLING OF EVAPORATION AND FREEZING PROCESSES AT THE MARTIAN SURFACE UNDER DIFFERENT ATMOSPHERIC PRESSURE AND ANNUAL AVERAGE TEMPERATURE CONDITIONS. THIS WILL CONSTRAIN MINIMUM WATER DELIVERY RATES FROM TWO POSSIBLE SOURCES: GROUNDWATER AND PRECIPITATION/SNOWMELT. WE WILL USE DARCY S LAW TO FIND CONSTRAINTS ON AQUIFER PROPERTIES THAT PERMIT THE RAPID FILLING OF A CRATER WITH WATER. WE WILL ADAPT OUR EVAPORATION/FREEZING MODEL TO ADDRESS THE STABILITY OF A BODY OF CRATER-FILLING ICE TO CONSTRAIN THE ANNUAL AVERAGE DELIVERY RATE OF WATER BY PRECIPITATION CONSISTENT WITH CRATER OVERSPILL. CHARACTERIZING POTENTIAL WATER SOURCES FOR FILLING POLLYWOG CRATERS WILL CONSTRAIN MARS CLIMATE HYDROLOGY AND THE GEOMORPHIC ROLE OF WATER AFTER THE VN FORMING PERIOD IN THE LATE NOACHIAN/EARLY HESPERIAN WHICH ADDRESSES GOAL II INVESTIGATION C2.1 OF THE MARS EXPLORATION PROGRAM ANALYSIS GROUP (MEPAG) MARS SCIENCE GOALS OBJECTIVES INVESTIGATIONS AND PRIORITIES: 2020 DRAFT: FIND AND INTERPRET SURFACE RECORDS OF PAST CLIMATES AND FACTORS THAT AFFECT CLIMATE.