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We present an inventory of alluvial fans and deltas within martian impact craters based on a systematic global survey of Context Camera images. Our database includes 314 fan‐hosting craters, with a total of 890 alluvial fans and 114 deltas. Alluvial fans and deltas are more widespread than previously reported (∼40°N to 54°S) and are strongly banded with respect to latitude. Most craters with alluvial fans occur at higher elevations (10°S–30°S) and along the dichotomy boundary (0°–10°N). Deltas occur at lower elevations (0°–40°N) where access to groundwater may have enabled the formation of lakes, and to a lesser extent in the highlands (0°–30°S). Alluvial fans in southern mid‐latitude craters preferentially formed along the northern and southern walls, which may reflect climatic control through solar insolation. The widespread distribution within the observed latitude bands and the similar Hesperian to Amazonian age of alluvial fan‐hosting craters is consistent with late‐stage synoptic precipitation. Plain Language Summary: Martian alluvial fans and deltas are intriguing features because they provide evidence for surface water and a climate that was very different than the present‐day conditions. This study presents a planet‐wide catalog of craters that host alluvial fans and interpreted deltas to understand where and when they formed. We systematically searched images from the Context Camera because this data set has the necessary resolution and coverage to identify and classify the landforms of interest. Our inventory of 314 craters with 890 alluvial fans and 114 deltas shows that these landforms are more numerous and widespread than previously reported. The similar age and distribution of craters with alluvial fans in the southern mid‐latitudes is consistent with a late occurring, widespread (rather than local) source of water. Craters with deltas are preferentially located at lower elevations where interactions with groundwater may have enabled the formation and persistence of lakes. Key Points: Craters with alluvial fans and scarp‐fronted fans (putative deltas) are more numerous than previously reportedThe widespread distribution of craters with alluvial fans in observed latitude bands is consistent with late synoptic precipitationFormation of alluvial fans in southern mid‐latitude craters on northern and southern walls may be influenced by solar insolation patterns [ABSTRACT FROM AUTHOR]

Estimates of river paleodischarges have been used to constrain the former climate of Mars. Paleodischarge has been calculated using mechanistic approximations of the channel bed‐shear stress at the threshold of particle motion or correlative width‐discharge relations derived from empirical terrestrial hydraulic geometry data. We apply both these methods to a study set of gaged terrestrial rivers with field‐measured bankfull properties to assess the reliability of discharge estimates given similar uncertainties as ancient martian rivers. We find that the threshold method yields conservative values, provided a reasonable grain size is used. However, we find that digital elevation models of a similar resolution to those constructed from Context Camera (CTX) data may not be of sufficient resolution to be useful for estimating paleohydrologic conditions. Results from our analysis demonstrate the inherent uncertainties when approximating paleodischarges on Mars and stress the need to consider realistic boundary conditions when determining such values. Plain Language Summary: The amount of water, or discharge, that flowed through martian rivers can be used to understand the planet's former climate. Various methods have been used by researchers to estimate martian river discharge, including relating river width to discharge or calculating the water volume required to move sediment in the river, but it is uncertain which of these provide more accurate results. We applied these same methods to rivers on Earth that have field‐assessed flow rates. We find that using grain size yields conservative discharge values, which is generally more desirable, but that there is significant uncertainty associated with both methods. Key Points: Two methods of estimating martian paleoriver discharge are applied to terrestrial rivers with known bankfull dischargesThe threshold approach yields more conservative discharges when used with realistic grain sizes and high‐resolution topographic dataUncertainties inherent in both methods emphasize the need to consider realistic boundary conditions when applied to Mars [ABSTRACT FROM AUTHOR]